Hey Ted,
My understanding of why these twelve are seen more often then others with these backs is that the group of twelve is broken down into smaller groups that are likely used in combination with a base group of 28 players across a 34 card sheet. Two rows of seventeen.
It is also likely that these twelve could have been printed multiple times across a sheet taking up more then one space. Giving a higher ratio compared to the base 28 group.
Take Group 1 below and split it across two 14 slot rows A&B and combine them with any of the Group 2, 3 & 4 players. For every unique 14A card there are 2 Duffy's.
14A + Devore + Duffy + Ford
14A + Devore + Duffy + Ford
14A + Devore + Duffy + Ford
14A + Devore + Duffy + Ford
14B + Devore + Duffy + Ford
14B + Devore + Duffy + Ford
14B + Devore + Duffy + Ford
14B + Devore + Duffy + Ford
For Red Hindu T206resource has a possibility of 46 combinations for this back. They can be broken down into the following groups of 28+12+6. The base 28 group can then be combined with any of the 6 base groups in any combination to form a 34 player sheet.
If the SuperPrints pop reports are lower with these backs it's possible they were used less frequently with the base 28 cards then your Exclusive 12.
From what I can tell, the entire 460 series backs can be broken down to multiple 28 base groups to combine with these three 6 base groups to form a 34 card sheet. Some backs use the Exclusive 12, some only use the SuperPrints (BL460) and some use both. Some use this base 28 or one of the other 28 groups.
Red Hindu groupings.
