ny_inflation_refund_credit assigned to wrong tax year (2025 instead of 2023)

[PavelMakarchuk]

Summary

ny_inflation_refund_credit is modeled as a 2025 refundable credit using 2025 NY AGI, but the actual program is based on 2023 tax year returns and paid as direct mailed checks — not as a credit on the IT-201.

This causes PE to overstate the 2025 NY refund by $150–$400 for every eligible filer, and understate the 2023 refund by the same amount.

Related TAXSIM issue: PolicyEngine/policyengine-taxsim#788

Evidence

From the official NY Tax Department page:

• Eligibility: "for tax year 2023, you: filed Form IT-201"
• Income used: "2023 New York Adjusted Gross Income (Form IT-201 line 33)"
• Delivered as mailed checks, not claimed on the IT-201

Root Cause

• formula_2025 in ny_inflation_refund_credit.py computes the credit using ny_agi for period 2025
• The credit is included in refundable.yaml for 2025-01-01
• Per PE convention, one-time rebates should be assigned to the tax year whose liability determines the amount — that's 2023, not 2025

Suggested Fix

1. Change formula_2025 → formula_2023 and formula_2026 returns 0 → formula_2024 returns 0
2. Move ny_inflation_refund_credit from the 2025 entry to the 2023 entry in refundable.yaml
3. Update existing tests to use 2023

Integration Test

- name: NY inflation refund credit - HoH 20K wages - should be in 2023
  period: 2023
  input:
    people:
      person:
        age: 54
        employment_income: 20_000
      child:
        age: 2
    tax_units:
      tax_unit:
        members: [person, child]
    households:
      household:
        members: [person, child]
        state_fips: 36
  output:
    ny_inflation_refund_credit: 200

- name: NY inflation refund credit - should be zero in 2025
  period: 2025
  input:
    people:
      person:
        age: 54
        employment_income: 20_000
      child:
        age: 4
    tax_units:
      tax_unit:
        members: [person, child]
    households:
      household:
        members: [person, child]
        state_fips: 36
  output:
    ny_inflation_refund_credit: 0