terminate 401k/SH... start SIMPLE IRA in the same calendar year?

I know that SECURE 2.0 allows you to terminate a SIMPLE IRA and start a 401k/SH plan in the same year after 1/1/24 (got to love those pro ration calculations!), but what about the other way around?  The fact that I'm not finding that you CAN do it makes me think it's not allowed.  Thanks.

Why are those few months really needed? Can’t we all just wait until January 1?

As far as I know, you can't do it. But I'm going from memory - I didn't go back and specifically check.

12 hours ago, Bill Presson said:

Why are those few months really needed? Can’t we all just wait until January 1?

Because clients don't understand things and some advisors won't listen to reason?  I agree that's the better solution.  My best guess is that they want to get out of the safe harbor nonelective as fast as possible and go to the SIMPLE IRA with match because almost no one defers.

2 hours ago, Belgarath said:

As far as I know, you can't do it. But I'm going from memory - I didn't go back and specifically check.

It's SECURE 2.0 Section 332.  The name of the section is "employers allowed to replace simple retirement accounts with safe harbor 401(k) plans during a year", but not vice-versa.  

Ok - yes, I went back and looked at it, and I agree - no dice. So even though there's no successor plan problem if a 401(k) is terminated and a SIMPLE-IRA plan is established, you still have the prohibition on establishing a SIMPLE-IRA plan (let's say for 2024) if the employer maintains during any part of the calendar year (2024) a qualified plan with respect to which contributions are made...

Curious as to whether it would be more beneficial to keep the 401(k) for the balance of this year, and switch to a safe harbor match for 2025? Are the HCE's deferring, or do they want to defer at a high level? If so, seems like the SH match would work better, if almost no one else is deferring? Facts and circumstances...