Plan number on document and 5500 do not match

We took over a 401k plan that has an adoption agreement that shows plan number 001.  However, the 5500 filing shows the plan as having plan number 002.  Apparently 001 was an old DB plan that is now terminated.  This goes back many years - at least as far back as 2008 I can see that the document and the 5500 have not had the same plan number.  The 5500s are correct - the plan document is incorrect.  How do we correct for the wrong plan number on the document?  We can fix the plan number on the upcoming Cycle 3 restatement - do I have to go back and correct for prior documents?  This plan started in 1990, I don't know if the document has always been wrong or what...   Thanks!

1 hour ago, AKconsult said:

We took over a 401k plan that has an adoption agreement that shows plan number 001.  However, the 5500 filing shows the plan as having plan number 002.  Apparently 001 was an old DB plan that is now terminated.  This goes back many years - at least as far back as 2008 I can see that the document and the 5500 have not had the same plan number.  The 5500s are correct - the plan document is incorrect.  How do we correct for the wrong plan number on the document?  We can fix the plan number on the upcoming Cycle 3 restatement - do I have to go back and correct for prior documents?  This plan started in 1990, I don't know if the document has always been wrong or what...   Thanks!

Just fix the plan number on the document now.  As it's an AA, an amendment would be appropriate. Nothing else needs to be done since the more important thing is that the 5500s appear to have had the correct number.

2 hours ago, Larry Starr said:

Just fix the plan number on the document now.  As it's an AA, an amendment would be appropriate. Nothing else needs to be done since the more important thing is that the 5500s appear to have had the correct number.

Well, in my experience, there is one more important task:  put a hardcopy note in your hardcopy file of the forms, describing what you are doing, why, and when.  It's OK to to also use an e-note, but it's best to have a note that is handwritten, dated, and signed.  (If you've ever found such a note in a file, you will understand how much credibility it carries.)  Do not rely on anyone's memory!  If there is a plan audit, make sure the auditor gets an explanation.  

Thank you both!!

And don’t forget to revise the summary plan description.  The plan identification number is an element of the required contents of a summary plan description.  29 C.F.R. § 2520.102-3(c).