Overstamped SM300 case backs

There are numerous overstamped 166.024/165.024 case backs and I think this is another version. One was called into question on another thread, suggesting it had been manipulated by a third party.
Well here is another example which would suggest this is a factory made marking to me. Both have the SP2 stamp of which I am not sure of the significance? I would guess it is like the SP on Speedmaster cases, just an indication of water resistance. Opinions @kox @speedamatuer


Ist version



2nd example