Here is the online catalogue from that Heritage auction. Only one lot mentions "Endicott" in the description (lot 10745), but a bunch of the T206s are from the Endicott, NY find, as you can see if you click on the lot numbers and look at the cards. The near-set of Sovereign backs do not have the "Endicott" designation on the flips (at least, the cards they showed do not), nor do the Lenox back or the Plank.
https://sports.ha.com/c/catalog-prin...Catalog-071515