I like to collect and if I see a copy of a record I have I tend to get another copy, a weird affliction I know but I do find that they are never the same, Never, they may look alike but they will sound different and then they can also look different, same matrix but different thikness plastic.
I bet this could be that at the pressing plant you have different makes of machine so they have different tolerances and if a stamper presses 500 you will need a few stampers to complete an order of say 5000
I wonder when records turn up in say 25 and 50ts and are warp is this because they have always been warped and that they were retuned to the manufacture??