Retroactive New Plan and Deduction Timing

I would appreciate any thoughts on the following two situations:

1. Employer wants to adopt a new PS plan in 2023 retroactively to the 2022 plan year (today's timing I realize is bad, but in theory). If the employer timely filed its 2022 tax return on March 1, 2023, and did not request/receive an extension, can the employer on, say, August 1, 2023, adopt a plan effective January 1, 2022, and contribute and deduct a 2022 PS contribution on August 1, 2023? The employer would have to amend its 2022 return, but is it permissible?
2. Employer wants to adopt a new PS plan in 2023 retroactively to the 2022 plan year. The employer did receive an extension until September 15, 2023, to file its 2022 tax return. The employer filed its 2022 tax return on July 1, 2023. Then, on August 1, 2023, the employer adopts a new plan effective January 1, 2022, and makes a contribution on August 1, 2023, that it would like to deduct for 2022. Can the employer amend its 2022 return to claim the deduction?

My guess is that 1 is bad and 2 is good, since the tax deadline is not 9-15 in the case without an extension.

#1 is no. The Plan must be timely adopted. Since there was no extension the deadline to adopt has already past. Either 3/15/23 or 4/15/23 depending on the type or tax payer and assuming calendar year filer.

#2 I believe is yes as long as the Plan is adopted by the extended due date and the contribution is deposited by the extended deadline; you'd just file an amended return. If it were a plan subject to minimum funding it might have an earlier deadline to avoid the 10% excise tax for failure to timely meet minimum funding.

I think both of these sets of facts have been discussed here on benefitslink with citations to support each in recent months but I'm too lazy to search.

Agree 100% with the above: #1 - NO, #2 - YES.

Thank you all.