I have worked with some people in the defence industry who got just that from Adobe and a few similar vendors. They had to negotiate with adobe and sign NDAs both ways, and they payed through the nose for it. But you can do it.
But having an older version can be useful too because some features from previous releases may be missing in current ones, so that's a way to ensure access to the old files. A couple of years ago all the Pantone colours used in Photoshop just became black after an update because Adobe stopped licensing Pantone stuff.
I worked at a large project management app where we charged per-seat.
We only offered per seat pricing, yet we had at least 3 companies that had flat pricing because they wanted >100k seats.
Deals outside of standard pricing gets cut all the time.