I've been watching this discussion, and I don't see what the problem is. I think you are worrying unnecessarily.
dmertz said that the value on the date of the rollover is what the brokerage is required to report on the Form 5498. It sounds like they are doing it correctly.
Why is this a "roadblock"? The distribution and the rollover took place in 2020. You don't have to do anything about it until you file your 2020 tax return next year. You don't need to know right now what the brokerage will put on the Form 5498. You'll find out when you get the 5498 in January. And even then it doesn't really matter. dmertz and macuser_22 told you that your 2020 tax return will use the distribution amount from the 1099-R, no matter what the brokerage puts on the 5498.
If you do need "proof" for the IRS, what you will need is the confirmations or statements from the brokerage showing that the distribution and the rollover were in-kind shares of stock, and that the shares were the same. Just save all your records related to the distribution and rollover.
