The thing to remember is the QC of these factories... as said above....
Sometimes you will pick up a version that is pretty much WP... however it is common to see missing or incorrectly sized O ring in the CB, CG etc even just simple lubing... so never ever assume any rep is WP
You should from a good practice POV get every rep srviced within a short time of having them... so when doing that have them pressure tested and dealt with if needed... you only have to look at threads on here and other forums to see just how dirty these movements are let alone poorly built in a lot of instances...
Even these latest AP V3 divers are coming out the factories without correct O rings etc
There is a steam test that can give a quick idea of things but I wouldnt recommend it to the uninitiated..