5500-EZ for 2022 not extended

We have tax client (not a TPA client) who we just discovered had plan assets exceeding $250,000 as of 12/31/2022 for the first time and it is an owner-only plan.  This is a Sch C client who has his 1040 extended and so taxes are due Oct 15.   We didn't know about this in July so we did not file an extension (nor were we engaged on the plan.)

We've never filed 5500s under the extended tax return rule.  I'm reading that as long as the plan year and tax year are the same and as long as the 5500 is filed by the tax return due date including extension, it is not late.  I want to be 100% on this since I don't want to risk missing the $500 penalty opportunity and risk a much larger late filing penalty which will then be blamed on us.

Thank you

Definitely appropriate to do it that way.

I thought the automatic extension only gave them until 9 1/2 months after the plan year end...meaning 9/15 even if tax retun is due 10/15.

Is that incorrect? 

September 15 is only 8 full months (through August) plus a half.  

9.5 months from 12/31 is the middle of October.

If you want to dot all the "I"s and cross all the "T"s request a copy of the client's tax return extension for your files. We've had to do this a couple times over the years and have never had an issue.