if one has a z visa, does one need to register for a yellow permit as well? case scenario: yellow permit obtained upon arriving in shanghai, work and residence permit (the passport like thing) obtained after a few weeks, but yellow permit submitted to entry/exit bureau and was never returned. thanks.

technically, yes.

always have one on hand. will save time and trouble later. you won't always need it, but the time you don't have it is the time that it will be required.

If you're smart you apply for a B-card as well, makes it a lot easier if you get stopped by the police and asked for ID.