Sorry that my reply to you is late, but responding to your......
" The red Hindu, red portrait Cobb above, which I remember was in a Mastro auction about ten or eleven years ago, looks
good to me. I don't see any glaring reason to suspect it is re-backed. "
Please check-out this Red HINDU card's scan, and strictly from its appearance, tell me if you suspect that it is re-backed ?
http://www.t206museum.com/page/periodical_23.html
Incidently, this Red HINDU Matty was graded about 10 years ago, same time you saw the Red HINDU Cobb in Mastro's auction.
Is that just mere coincidence ? ......I don't think so !
Furthermore, several years ago, these two graded T206 Cobb's were sold.
Cobb (Green portrait) with a Red HINDU back
Cobb (Bat OFF) with a PIEDMONT 150 back
Jim....need I say more ? ?
Best regards,
TED Z