Can employer deduct 2021 ACP Safe Harbor Match on 2022 Tax Return?

Employer (S-Corp) extended its 2021 Tax Return to 9/15/2022, however filed it in April.

In March, 2022 the Employer deposited its Safe Harbor Matching (ADP) contribution for the 2021 Plan Year. This contribution was deducted on its 2021 tax returns.

On September 15, 2022 the Employer deposited its Safe Harbor Matching contribution for the 2021 Plan Year and since it had already deposited the requisite ADP Safe Harbor Match would like to deem it the ACP Safe Harbor Match (as permitted by the Plan).  Q: Can this contribution be deducted on the business' 2022 tax returns or must the 2021 returns be amended to capture the deduction? The amount is well below 404 deduction limits and it is anticipated it will be well below the 2022 404 deduction limit if added to the 2022 plan year contributions.

There are differing opinions on this, but my opinion is yes. Under IRC 404(a)(6), the contribution deemed to have been made on the last day of the prior taxable year if it is made "on account of such taxable year." Clearly it was made on account of the prior plan year, but what does it mean to be made on account of the prior taxable year? The IRS doesn't elaborate, but the only thing that makes sense to me is that the employer deducts it on that year's tax return. Since they didn't do that, I would argue that it defaults to being deductible in the year contributed (assuming it meets all the other requirements to be deductible, of course).

Thank you for your thoughts on this.  This is what I was thinking, too.  The amount involved is less than $20,000. If amending returns for 2021 to capture the deduction, it would involve amending 4 returns (s-corp) and so the next thought was to just deduct it in 2022 (year deposited) even though a 2021 annual addition to the Plan. I read through a number of articles and even guidance but none that I read seemed to address this specifically (timely deposited just not deducted). Those who benefited from the contribution are employed in 2022 so there is no expectation of 404 or 415 issues.