What's current state of adult paperwork for content producers?
 

What's required by US/EU law and what's the practical way to keep track of paperworks for content producers?

In what cases content produces might be required to provide paperwork?

Google 2257 for the US. Lots of VERY specific detailed rules, with paperwork being open to inspection at the posted location. Here's a good Q&A, tho it hasn't been updated to account for Jeff Sessions.

Ten Frequently Asked Questions About The 2257 Regulations