Wrong PN on 5500-EZ for years

Employer had IRS Plan Number 003 terminated in 2003 and started PN 004 in 2004.

I don't know what year they started filing the 5500-EZ, but I'm guessing it was a bunch of years ago.  I see letters in my files going back to 2018, but I only have the EZs going back to 2015.

The ones I have are all PN 001, so I'm assuming all the others are, too.

What's the fix?  Can I just fill out question 4 and change the PN there?  I'd rather not amend 15 years worth of forms.

Its been a while, but I have contacted the entities division at IRS in the past.  I don't have the number available, but I believe you fax them with a request to change the PN, with an explanation, and they fix it in their records for multiple years.  I had to do it for several clients after the IRS took it upon themselves to change the PN for several of my plans in 2014 or 2015.