There was a lot of confusion early on that hasn't been fully cleared up, no matter what anybody says.I don't get that people are expecting 99% compatibility of PS4 games. I've only heard them saying that they are shooting for the top 100 PS4 games. That's it. No full PS1, PS2, PS3 compatibility and not 99% PS4 compatibility.
They have said repeatedly that they expect the vast majority of PS4 games to play on PS5. The 99 per cent quote came from Jim Ryan a couple of weeks ago. He was talking about the games they've tested.
I'm not so sure they mean at launch. I suspect there will be a whitelist of a few hundred to a few thousand titles at launch, with constant updates as they tweak their system. There won't be any enhancements to the vast majority of titles except to loading times, where they'll be similar to the Series X stuff.
Anything better than this will be amazing, but I'd rather set myself up for disappointment.