This is really long and likely not interesting to most but here goes.
The 34 SC150F649OP backed subjects look to be, for the most part grouped together for several backs. It would make sense that several of these sheets were selected to be used with F649 packs. At some point were overstruck.
The F42s are a bit more complex and very interesting to study. The theory is that some sheets were selected to be F42OP and some F30.
At one point 109 SC460F30 cards were printed however only 52 made it into the wild, the rest being overprinted.
These 52 are comprised of a base group of 34 cards (these 34 are in every 460 back except for P42). In addition to the 34 any of Teds Exclusive 12 (broken into groups of 6 or smaller) and the 6 super prints could be substituted in to those 34. This allows for several possible combinations of 34. Doubling up the Exclusive 12 into the base could get us the higher percentage that we see making them "Exclusive".
That leaves 57 (109-52) original F30s that were at some point overprinted to F42 that never showed up in the wild as F30. Well some did but not in packs
see further down.
This 57 is based on two 28 base groups and a second printing of one swapping out Dougherty with Ames hands above head. 28 + 28 + 1 = 57. Some 460 backs have Ames, some have Dougherty and some have both.
Now those 28 base groups in combination with the Exclusive 12 (broken into smaller groups of 6) and the 6 super prints allow for multiple combinations of 34. The Exclusive 12 again could have been doubled up and swapped into the base 28 to get a higher percentage of those 12.
These combinations of 34 are found in every 460 back except for Sov 460, which uses the earlier mentioned base of 34+12+6 (identical to SCF30).
The theory is that some sheets were selected to be F42OP and some F30.
Lucky enough a wonderful thing happened. One sheet of 34 F30 destined to be overprinted, a 28 base group and the 6 super prints was scrapped mid print and never overprinted.....these are known as the yellow brown scraps. Every known example fits into one base group of 28 + 6 superprints. There are 1-3 examples of each, with one having four. This fits into the theory that multiple stacked examples of each card was used.
The base 28 yellow browns are special as they have a F30 back that never made it to the overstrike machine, technically ALC never intended them to get out. Pretty cool.
And, this is just my theory.