My understanding is that Century started denoting the WASR-10 as 10/63 when they began using milspec parts kits, perhaps because these kits were typically part of a Romanian PM.63/65 in their former lives. Some also appear to be sourced from Guardia "G" kits as well, which were technically semi-auto only versions of the PM.63/65.
WASRs were originally built from either armory rejected or "new" parts kits, notably having a front trunnion with no armory approval stamp (triangle or triangle/arrow). The front trunnion on these non-milspec kits apparently sometimes had less or weaker material than the milspec trunnions, and sometimes suffered from failure of the locking lugs.
I have a 10/63 built from a 1978 milspec kit. It has no bayonet lug (the ears are ground off) and the muzzle nut was originally welded on, but has since been removed. The barrel was properly threaded 14x1LH and did have a detent pin in the FSB. Despite having these features that are believed to be indicative of a WASR-10, the rifle is still clearly marked 10/63 on the receiver.