Can we say before this date, if your submitted games don't work properly on ps5 during cert, Sony will have to tidy things for you.
After this date, if your games fail ps5 cert, Sony throws it back at you to tidy things?
As for MS because of virtualization, either scenario should be a smaller tweaks at either ends to pass certification. Or in other words, both scenarios won't happen because it just 'work' , to a certain dev friendly degree
No. MS, Sony and Nintendo certification always worked in the same way for all generations: you submit a game to be published, they test if it fills all their checklist (which may change over time) making sure doesn't have certain type of bugs. If the game doesn't pass that you need to fix it submit the game again.
It's quite common that they even check if the game works in different skus of the same generation: different revisions with the same supposed hardware sometimes cause bugs in a SKU but works in another that is supposed to be the same console. This 'is just works' you mention is bullshit, this 'virtualization' is not a magic thing. Like with anything else, games also experience issues within it.
The only change they added here is another thing to the ckecklist that games submitted to be published on PS4 have to fullfill. Devs now will have to check it works in a PS5 and if doesn't work the dev has to fix it. They did the same when added new consoles like Slim/S/Pro/X/SAD/Series X/etc.
PS4 games released before were submitted without checking if it did work in a final PS5 devkit because it didn't exist so they weren't able to do it. So Sony is checking if the already submitted PS4 games work well there. For those that doesn't work, Sony suggest them to fix these PS4 games to make them run on PS5 because Sony can't change the code of the non-Sony games, and until fixed aren't added. This is why in BC (not only in Sony, also in MS and Nintendo) there are almost always some games -or a lot- that aren't supported or added to their BC stores (in this later case is more complex because there are also legal issues with rights/licenses/etc that sometimes prevent that game being released on more platforms or after a certain period of time).
