The #55 definitely had 3 design revisions per nhplaneparts: A "long sliding nicker", a "shorter sliding nicker" (with lower threaded hole position on the skate), and then finally the "cloverleaf nicker". I *thought* (based on nhplaneparts again) that the same was true for the 45, but it may be that it only used one or the other of the two sliding variants before moving to the clover-leaf design. That would seem odd considering that the 45 predated the 55 in production, though.
Steve, we've already established that you have a newer 45 and that it and its irons differ from older ones. This is one of those differences.