The PS1 GPU is a bit easier than something like the the SNES to get to the compat to meet their goals since it really doesn't encourage 'racing the beam' style

The PS1 GPU is a bit easier than something like the the SNES to get to the compat to meet their goals since it really doesn't encourage 'racing the beam' style techniques. It's a more modern design which runs scanout asynchronously from drawing using a relatively large VRAM buffer between them. For anything other than emulating absolute batshit demoscene level code, you can get away with just being in the right ballpark for how long drawing a frame takes. And apparently they were OK with blacklisting a few of the problem titles.