"Can a company with over 100 employees sponsor a SEP?"

"Sole-prop situation with the CB Plan. The minimum for 2022 is 160K, the client has made only 150K contribution in 2022 for 2022 Plan Year. CPA went ahead and has already filed the tax return for 2022 without consulting with anyone. Per my conversation with the advisor, the 'missing' 10K has been deposited today. My understanding that reliance on revenue ruling 76-28 still secures the deduction of that 10,000 for 2022 tax year as long as the tax return is refiled. [1] Anything I might be missing here? [2] Reliance on 76-28 requires a designation in writing by Sponsor to Plan Administrator of that contribution as being made for 2022. Does anyone has a sample of such language they would be willing to share? [3] Tax return will have to be amended -- I do not believe it needs to be amended by 4/15 and can be really amended at any point. Thoughts?"