So if they’ve been confiscated ghost guns, what did they need this law for?

https://denver.legistar.com/View.ash...7-AB8720C8C05A

I see the words for the definition of a receiver, but I don’t know how that actually fits into the wall? So you can still work in an 80% receiver but as long as you put a number on it it’s OK? Or does that mean you have to file some ATF paperwork?