I've practically given up on relying on taxpayer's knowledge for any of this stuff.  I literally just got off the phone with someone who made a $6K Roth contribution back in April.  The 5498 won't be ready until May and he said he could "only download transactions in csv format."  "How about a monthly statement for April 2021?"  Surprise, he could get one of those and lo and behold it shows a $6K contribution to an account identified as a Roth IRA and, bonus, a TY designation of 2021 right there on the statement.  So I have everything that I would have gotten from a 5498 all in one place and we don't have to wait until May.

Moral of the story, there are broker statements somewhere that will tell you what actually happened and when.  Follow the breadcrumbs.

Rick