Leon, my Heinie Heitmuller is the one with the ad back, and I too had noticed when you see a HRK w/ an ad back it tends to be Heitmuller as well.
On a similar note, in the 1912 Zeenut set I have seen more Otto Auer cards with the Zeenuts ad back than other cards in the set. Anyone else notice this?
-Rhett