ADP/ACP question (union / non-union)

401(k) plan with a 1/1 to 12/31 plan year, union and non-union employees, and they utilize the prior year testing method. In 2024, an ADP test is completed separately for union and non-union employees, due to the mandatory disaggregation rules. An ACP test is completed for the non-union employees (union group deemed to pass ACP).

On 1/1/2025, the union is dissolved/decertified. All union employees are now considered non-union effective 1/1/2025. 

So for 2025, there is just one ADP/ACP test (given that all employees were non-union in 2025). When determining the prior year percent for the ADP test - is there any guidance on what to use? Do you just use the 2024 non-union NHCE average and disregard the 2024 union NHCE average? Calculate a weighted average? If a weighted average should be used, then how would you go about determining the NHCE average for the ACP test? (given that there was no ACP test in 2024 for the union group)

Personal opinion is you use only the non-union prior year ADP and ACP. Those are numbers for the disaggregated component plans and you still have that for non-union, just a larger population for 2025.

Look at it this way, what if union covered employees were excluded from the plan before, now enter 1/1/2025 when union is dissolved. Is there any question you'd use the 2024 ADP and ACP from those (non-union only) participants? 

You look at that union disaggregation as if it was a separate plan.