diff --git a/R/clean_lab_main.R b/R/clean_lab_main.R
index 8489980..21a5451 100644
--- a/R/clean_lab_main.R
+++ b/R/clean_lab_main.R
@@ -22,6 +22,13 @@ clean_lab_main <- function(dataset, list_analyses = c(), lab_target_units, lab_u
   meta_unit_conv <- data.table::fread(lab_unit_conversion)
   meta_thresholds <- data.table::fread(lab_thresholds)
 
+  requested_datasource <- datasource
+  if (requested_datasource != "" && "datasource" %in% names(meta_unit_conv)) {
+    meta_unit_conv <- meta_unit_conv[
+      is.na(datasource) | trimws(as.character(datasource)) == "" | datasource == requested_datasource
+    ]
+  }
+
   # If list_analyses is empty, use all concept_ids from target units
   if (length(list_analyses) == 0) {
     list_analyses <- unique(meta_target_units$concept_id)
@@ -97,7 +104,10 @@ clean_lab_main <- function(dataset, list_analyses = c(), lab_target_units, lab_u
     # For compatibility with mo_convert, rename unit_origin to unit_matched
     setnames(meta_cid_full, "unit_origin", "unit_matched", skip_absent = TRUE)
     # Step 4: mo_convert with full metadata (unit conversion and thresholding)
-    dt_cid <- mo_convert(dt_cid, meta_cid_full)
+    dt_cid <- mo_convert(
+      dat_unit_matched = dt_cid,
+      metadata_convert = meta_cid_full
+    )
     dt_cid[, value := data.table::fifelse(included == 1, value_converted, NA_real_)]
     dt_cid[, unit_target := target_unit_cid]
 
diff --git a/R/mo_convert.R b/R/mo_convert.R
index 1fcbd98..6a22742 100644
--- a/R/mo_convert.R
+++ b/R/mo_convert.R
@@ -141,7 +141,7 @@
   list(success = FALSE, tried = 1L)
 }
 
-.mo_try_missing_chain <- function(dat, i, attempts, val_raw, conv_success = 3L, other_flow = FALSE) {
+.mo_try_missing_chain <- function(dat, i, attempts, val_raw, conv_success = 3L, other_flow = FALSE, skip_assumed_unit = NA_character_) {
   # Returns list(success=TRUE/FALSE, tried=number_of_attempts_tried)
   tried <- 0L
   # explicit next_attempt chain (>0)
@@ -170,6 +170,13 @@
   }
   # rows labelled as missing
   missing_rows <- attempts[unit_matched == "missing"]
+  if (!is.na(skip_assumed_unit) && nrow(missing_rows) > 0 && "assumed_unit_if_missing" %in% names(missing_rows)) {
+    missing_rows <- missing_rows[
+      is.na(next_attempt) |
+        next_attempt != 0 |
+        .mo_norm(assumed_unit_if_missing) != skip_assumed_unit
+    ]
+  }
   if (nrow(missing_rows) > 0) {
     for (r in seq_len(nrow(missing_rows))) {
       attempt_row <- missing_rows[r]
@@ -273,42 +280,38 @@ mo_convert <- function(dat_unit_matched, metadata_convert) {
     missing_attempts_tried <- 0L
     if (origin_other) {
       row_unit_matched <- NA_character_
+      pref_res <- list(success = FALSE, tried = 0L)
       if ("unit_matched" %in% names(dat)) row_unit_matched <- ifelse(is.na(dat$unit_matched[i]) || dat$unit_matched[i] == "", NA_character_, norm(dat$unit_matched[i]))
       if (!is.na(row_unit_matched) && nrow(attempts) > 0) {
         pref_res <- .mo_try_prefilled_assumed(dat, i, attempts, row_unit_matched, val_raw, conv_success = 1L, other_flow = TRUE)
         missing_attempts_tried <- missing_attempts_tried + pref_res$tried
         if (isTRUE(pref_res$success)) next
       }
-      miss_res <- .mo_try_missing_chain(dat, i, attempts, val_raw, conv_success = 1L, other_flow = TRUE)
+      skip_assumed_unit <- if (pref_res$tried > 0L) row_unit_matched else NA_character_
+      miss_res <- .mo_try_missing_chain(dat, i, attempts, val_raw, conv_success = 1L, other_flow = TRUE, skip_assumed_unit = skip_assumed_unit)
       missing_attempts_tried <- missing_attempts_tried + miss_res$tried
       if (isTRUE(miss_res$success)) next
     } else {
       if (unit_missing_flag) {
         row_unit_matched <- NA_character_
         if ("unit_matched" %in% names(dat)) row_unit_matched <- ifelse(is.na(dat$unit_matched[i]) || dat$unit_matched[i] == "", NA_character_, norm(dat$unit_matched[i]))
+        pref_res <- list(success = FALSE, tried = 0L)
         if (!is.na(row_unit_matched) && nrow(attempts) > 0) {
           pref_res <- .mo_try_prefilled_assumed(dat, i, attempts, row_unit_matched, val_raw, conv_success = 3L, other_flow = FALSE)
           missing_attempts_tried <- missing_attempts_tried + pref_res$tried
           if (isTRUE(pref_res$success)) next
         }
-        if (nrow(attempts) > 0) {
-          miss_res <- .mo_try_missing_chain(dat, i, attempts, val_raw, conv_success = 3L, other_flow = FALSE)
+        # Only call the missing chain if prefill did not already cover the single attempt
+        # (i.e., prefill did not run, or there are chained attempts with next_attempt > 0 to pursue).
+        if (nrow(attempts) > 0 && (pref_res$tried == 0L || nrow(attempts[!is.na(next_attempt) & next_attempt > 0L]) > 0L)) {
+          skip_assumed_unit <- if (pref_res$tried > 0L) row_unit_matched else NA_character_
+          miss_res <- .mo_try_missing_chain(dat, i, attempts, val_raw, conv_success = 3L, other_flow = FALSE, skip_assumed_unit = skip_assumed_unit)
           missing_attempts_tried <- missing_attempts_tried + miss_res$tried
           if (isTRUE(miss_res$success)) next
         }
       }
     }
 
-    # 2) If unit missing (or flagged missing), try attempts ordered by next_attempt (for assumed units)
-    if (unit_missing_flag && nrow(attempts) > 0) {
-      # consider explicit next_attempt chain (>0) first, then any rows that encode MISSING regardless of next_attempt
-      # Try the missing-attempts chain (includes explicit next_attempt chain
-      # and any rows labelled as MISSING).
-      miss_res <- .mo_try_missing_chain(dat, i, attempts, val_raw, conv_success = 3L, other_flow = FALSE)
-      missing_attempts_tried <- missing_attempts_tried + miss_res$tried
-      if (isTRUE(miss_res$success)) next
-    }
-
     # 3) Fallback: try all attempts ordered by next_attempt (1,2,...) as fallbacks for conversion
     conv_success_current <- if (origin_other) 1L else if (unit_missing_flag) 3L else 1L
     other_flow_current <- origin_other
diff --git a/tests/data/Example 5/g_output/dataset_cleaned_output_lab_values.csv b/tests/data/Example 5/g_output/dataset_cleaned_output_lab_values.csv
new file mode 100644
index 0000000..601b1a5
--- /dev/null
+++ b/tests/data/Example 5/g_output/dataset_cleaned_output_lab_values.csv	
@@ -0,0 +1,5 @@
+person_id,concept_id,value_origin,unit_origin,included,value,unit_target,conversion,rule_applied
+P01,LAB_HBA1C,6,%,1,42.08,mmol/mol,1,1
+P02,LAB_HBA1C,42,mmol/mol,1,42,mmol/mol,0,0
+P03,LAB_HBA1C,70,%,1,70,mmol/mol,1,1
+P04,LAB_HBA1C,70,"",1,70,mmol/mol,3,0
diff --git a/tests/data/Example 5/i_ground_truth/dataset_cleaned_lab_values.csv b/tests/data/Example 5/i_ground_truth/dataset_cleaned_lab_values.csv
new file mode 100644
index 0000000..78ca7d6
--- /dev/null
+++ b/tests/data/Example 5/i_ground_truth/dataset_cleaned_lab_values.csv	
@@ -0,0 +1,5 @@
+person_id,concept_id,value_origin,unit_origin,included,value,unit_target,conversion,rule_applied
+P01,LAB_HBA1C,6.0,%,1,42.08,mmol/mol,1,1
+P02,LAB_HBA1C,42,mmol/mol,1,42,mmol/mol,0,0
+P03,LAB_HBA1C,70,%,0,,mmol/mol,1,90
+P04,LAB_HBA1C,70,,0,,mmol/mol,3,91
diff --git a/tests/data/Example 5/i_input/LAB_target_units.csv b/tests/data/Example 5/i_input/LAB_target_units.csv
new file mode 100644
index 0000000..3b55a55
--- /dev/null
+++ b/tests/data/Example 5/i_input/LAB_target_units.csv	
@@ -0,0 +1,2 @@
+concept_id,unit_target
+LAB_HBA1C,mmol/mol
diff --git a/tests/data/Example 5/i_input/LAB_threshold.csv b/tests/data/Example 5/i_input/LAB_threshold.csv
new file mode 100644
index 0000000..efe68bd
--- /dev/null
+++ b/tests/data/Example 5/i_input/LAB_threshold.csv	
@@ -0,0 +1,2 @@
+concept_id;Min;Max;unit_target;condition_on_variable;variable
+LAB_HBA1C;9;174;mmol/mol;;
diff --git a/tests/data/Example 5/i_input/LAB_unit_conversion.csv b/tests/data/Example 5/i_input/LAB_unit_conversion.csv
new file mode 100644
index 0000000..2075e95
--- /dev/null
+++ b/tests/data/Example 5/i_input/LAB_unit_conversion.csv	
@@ -0,0 +1,5 @@
+concept_id,datasource,unit_origin,unit_target,multiplication_factor_from_origin_to_target,conversion_not_multiplication,conversion_rate,condition_on_value,assumed_unit_if_missing,next_attempt
+LAB_HBA1C,,%,"mmol/mol",,(10.93 * value) - 23.5,,,,0
+LAB_HBA1C,DS_A,MISSING,"mmol/mol",,(10.93 * value) - 23.5,,,"%",0
+LAB_HBA1C,DS_B,MISSING,"mmol/mol",1,,1,,"mmol/mol",1
+LAB_HBA1C,DS_B,MISSING,"mmol/mol",,(10.93 * value) - 23.5,,,%,2
diff --git a/tests/data/Example 5/i_input/LAB_unit_conversion_no_DS.csv b/tests/data/Example 5/i_input/LAB_unit_conversion_no_DS.csv
new file mode 100644
index 0000000..cb5fe33
--- /dev/null
+++ b/tests/data/Example 5/i_input/LAB_unit_conversion_no_DS.csv	
@@ -0,0 +1,3 @@
+concept_id,datasource,unit_origin,unit_target,multiplication_factor_from_origin_to_target,conversion_not_multiplication,conversion_rate,condition_on_value,assumed_unit_if_missing,next_attempt
+LAB_HBA1C,,%,"mmol/mol",,(10.93 * value) - 23.5,,,,0
+LAB_HBA1C,DS_A,MISSING,"mmol/mol",,(10.93 * value) - 23.5,,,"%",0
diff --git a/tests/data/Example 5/i_input/dataset_lab_values.csv b/tests/data/Example 5/i_input/dataset_lab_values.csv
new file mode 100644
index 0000000..93c2961
--- /dev/null
+++ b/tests/data/Example 5/i_input/dataset_lab_values.csv	
@@ -0,0 +1,5 @@
+person_id,concept_id,value,unit
+P01,LAB_HBA1C,6.0,%
+P02,LAB_HBA1C,42,mmol/mol
+P03,LAB_HBA1C,70,%
+P04,LAB_HBA1C,70,
diff --git a/tests/test_clean_lab_temp.R b/tests/test_specific_example.R
similarity index 74%
rename from tests/test_clean_lab_temp.R
rename to tests/test_specific_example.R
index 295a26d..cf7fd78 100644
--- a/tests/test_clean_lab_temp.R
+++ b/tests/test_specific_example.R
@@ -1,32 +1,39 @@
-# Test script for clean_lab_main
-# This script will run clean_lab_main on all Example datasets and compare output to ground truth
+# Test script for debugging
+# This script will run CleanLabValuesDataset on an Example dataset, save the output and compare output to ground truth, if any
 
 library(data.table)
 # Load modular code
 source("R/load_dependencies.R")
 load_cleanlab()
 
-examples <- c("Example 4")
+examples <- c("Example 5")
 base_path <- "tests/data"
 
 for (ex in examples) {
   cat("\nRunning test for", ex, "...\n")
   input_dir <- file.path(base_path, ex, "i_input")
   gt_dir <- file.path(base_path, ex, "i_ground_truth")
-
+  out_dir <- file.path(base_path, ex, "g_output")
+  dir.create(out_dir, showWarnings = F)
+  
   dataset_lab_values <- fread(file.path(input_dir, "dataset_lab_values.csv"))
   path_lab_target_units <- file.path(input_dir, "LAB_target_units.csv")
-  path_unit_conversion <- file.path(input_dir, "LAB_unit_conversion_wrong.csv")
+  path_unit_conversion <- file.path(input_dir, "LAB_unit_conversion.csv")
+#  path_unit_conversion <- file.path(input_dir, "LAB_unit_conversion_no_DS.csv")
   path_lab_thresholds <- file.path(input_dir, "LAB_threshold.csv")
 
   # Run cleaning
   cleaned <- CleanLabValuesDataset(
     dataset = dataset_lab_values,
+    datasource = "DS_A",
     lab_target_units = path_lab_target_units,
     lab_unit_conversion = path_unit_conversion,
     lab_thresholds = path_lab_thresholds
   )
 
+  # Save output
+  fwrite(cleaned, file.path(out_dir,"dataset_cleaned_output_lab_values.csv"))
+  
   # Load ground truth
   gt_file <- file.path(gt_dir, "dataset_cleaned_lab_values.csv")
   if (file.exists(gt_file)) {