Nondiscrimination testing re the TIMING of contributions to two different groups

So, Employer A acquires Employer B mid-year. Employer A sponsors a safe harbor 3% 401(k) plan. Employer A credits all service with Employer B for all purposes. The result is that all employees of Employer B are immediately eligible.

What gets strange is that Employer A calculates and deposits the 3% SH each payroll (not by document provision, just by administrative choice). But for the former Employer B employees, not intentionally but through administrative error, the 3% was not deposited until after the end of 2023. (They corrected this for 2024, and everybody gets the deposit each payroll.)

The difference, due to the relative number of employees, would easily pass either a 70% test, or a benefits/rights/features test. Document doesn't specify a particular timing requirement. Yet I can't shake the feeling I'm missing something. Any thoughts on this?

You pass the 70% test so you are good.

Even if you didn't I might argue for transition relief in 2023 to test the timing separately with respect to each group due to the business transaction.

If this was on going, I'm not sure what the correction would be if you were failing the 70% test, but I'd guess giving lost earning to the annual deposit group due to timing would be an acceptable IRS fix.