Notice from @ 10:37 he carries two double racks with 4 bombs, not 4 bombs on 4 "stations" which are not the racks, but the rack stations, and he only designates 1 (PP1) program to 'STA 2 3 7 8' which is murky (compared to when carrying 8 and the symbology) but hey it works.
With 4 double racks and 8 bombs, the actual STA 2 3 7 8 carry the bombs 1 2 3 4 5 6 7 8 and can be deployed when making sure STEP first all 4xPP1, then all PP2, the STEP picks the 'next one' whichever.
One false click and you're stuck, hence the 'clear' button (that is WIP).
It seems, perhaps in RL also, a better way would have been to have STA (or something) designate the physical stations, to unclutter the mind, and have STEP show on the STORES the designated 1 or 2 per the physical station.
And prob TOO1 and TOO2 would be quite handy also.
Then again, life is a bitch.