A 5498 is for money In. That's informational and not part of tax reporting.

Did you get a 2020 5498 for a late rollover of 2019 money? The 1099-R would be issued for the money Out. As long as you reported it properly for what it was for your client, in 2019, the 5498 is confirmation of what they did with it, which you would confirm that is what they told you and what you filed on tax return.

In other words, confirm it really was a rollover, a conversion, or whatever they told you, is backed up by that 5498 for where the money ended up.