Yes, it is very unlikely that those will be found with an AB460 back. But, the engineer in me says that because this mutual exclusion principle (for 350/460 Series, fronts with AB460 backs will also be found with Uzit backs, but won't be found with BL460 or Red Hindu backs) is based on a sample of the population rather than the entire population of T206's ever produced, there remains a statistical (though perhaps very slight) uncertainty in the mutual exclusion principle.
And if we state that these will not be found with an AB460 back, then people will be less likely to look for them; thus reducing the chance of finding an exception to the principle if there is one. Kinda like in quantum physics where the act of observing affects the observation.
This is all the more important with T206 because exceptions to the rules have been demonstrated. Some examples include:
The 150 Only group does not have any Sweet Cap 150 Factory 649 Overprint backs
EXCEPT for Powers.
The 350 Only group has AB350 (Frame) backs
EXCEPT for Nichols Batting, which has an AB350 (No Frame) back.
The 350-460 group have all been confirmed with Piedmont 350-460 Factory 42 backs
EXCEPT for Tinker Bat Off.
And please understand that it is not my intention to demean your work in any way. We would not have achieved our current level of understanding of T206 without your efforts.
Always Best Regards
Craig