In both cases it appears to me that the SN on the butt socket has been added to match the number on the bolt, suggesting a spare receiver to which a bolt from a condemned receiver was mated. I don't think they threw much away at SAL and if they did there were probably people who salvaged as much as they could into their lunch boxes. I can remember a couple of estates from people who worked for similar crown corporations, DND-related, who seem to have taken home anything and everything that was being turfed, including some stuff you would have needed the canteen truck to move, rather than a lunch box.
If the rifle was made up for a friend of a friend sort of thing, the more impressive stamps added the better the recipient was probably going to like it.