Yes, the butt well as designed was to shallow for the standard K98 oiler, so they produced special short oilers to fit.
Later G/Ks have deeper wells and will fit a a standard oiler.
I have a ac 45 "c" block gun that still has the shallow well. Maybe it has a stock that was rejected earlier then salvaged. But did they make them out of plastic? Or were the short oilers all metal. Mine appears to be the same as my other plastic ones only a bit shorter.
I think this may be true, but Im thinking it very well maybe just variations in oiler productioin is all....Ive never studied or compared them though