Based on the gearbox ratios I got off another Wiki article, here are all the effective ratios for a TRQ-7220 Quadruplex. You can see where the ratios overlap, and would be skipped. You can also see why some of the LO-LO ratios would not be useful in a progressive sequence. Those could have been used, however, for "road speed control" for specific applications.
I have done this with lots of the other old transmissions as well, if anybody is interested.