What is the lifespan of plywood as roof decking?
I would give your business to one of the "is good and stays dry" roofers who are not blatantly trying to fleece you.

Now, the other two may be working from the assumption that if you bothered to call a roofer, you have leaks. But they strike me a lying scammers if they are selling you new plywood with no idea if the roof deck is rotten or solid.

Plywood does not have an expiration date.