Just curious, you are right !
Mauser used to take large ring/small shank actions when dovetailing the front receiver ring for a scope mount…but not “always”.
Like you, I have encountered small ring K type with the front receiver dovetailed and large ring/large shank actions factory dovetailed for the front mount plate.
However on the ones I have had in hand the cut didn’t go to the threads…but I can’t say that they “never” have done deeper milling.
There’s the rule and there’s the reality and when production demands they go to what they have on hands...

Best.

DORLEAC
www.dorleac-dorleac.com