Posted By:
Craig WHi Jamie,
I don't know what the multiplier is for blank backs, but this link has them as 10th hardest out of 40. Perhaps if you have the multipliers for Pied 350-460 Fact 42 and Lenox (black) you can estimate the blank backs.
http://www.t206guide.com/back_guide.htm
By the way, congrats on the T206 set you've assembled - it's quite an accomplishment!
Best regards,
Craig