I think it boils down to two things:
how recognisable the variety is (so ME, LT, H, KN fit that perfectly)
how rare it is (Gouby X, Open 3 fit that)
So the 1* obverse for 1908 is rare but not very recognisable, so a lot probably got missed. In that sense it's a "micro variety", i.e. tiny differences. However, the 1905 varieties don't fit either category being neither instantly recognisable nor rare, so don't float my boat at all.