The main differences between the scopes:
Mk1 has range increments of 50 yds & deflection increments of 2 moa.
Mk2 has both range & deflection increments of 1 moa. Earlier scopes have the same individual, mounted directly into the scope tube, ocular lenses; later Mk2's have the self contained eye lens assembly as per the Mk3 scope.
Mk3 scope has both range & deflection increments of 1 moa, the ocular lens cell, & totally redesigned drums to make them easier to adjust for zero.
Concerning backlash, the amount that occurs will depend on how worn the scope is, & whether it has any anti-backlash springs fitted. Mk1 scopes can be a right mish-mash in this respect; earlier unmodified scopes will have no anti-backlash spring at all. Later, a single spring under the grat block eased the situation in range only mode, & later still twin springs were fitted to the cursor that holds the grat block so as to eliminate the problem in both range & deflection.
Hope this helps a bit.