Great discussion. Quick note for the 350-460 series backs. There are several subgroups we see of 28 cards that combine with the 6 super prints to make 34. There are other 13+21 subgroups that are always together that also make 34. The entire 460 series cards all break down to groups that combine to 34. Some likely were done over multiple print runs with a few cards being swapped out which gives the appearance that 34 is not a constant.....but it is
As well by taking the SC350-460 cards and grouping cards that are found together with other backs we end up with several smaller groupings. One group of 28 F42OPs shows up that do not show up with F30 backs. Even though under the OP is a F30. This sheet of 28 + 6 super prints was never released as F30 and went straight to the OP machine. Pretty cool.
Fortunately a scrap sheet survived before being Over Printed and we get the 34 know examples of the yellow brown scraps. Only the 34, all but one have been found with no exceptions. This makes me happy