I thought it was the last 7 recordings 113 to 119 that were pressed up in lots of 2,500 following the success of the Epsilons. I've always thought this was a bit bazaar as Les Chansonettes 114 is relatively easy and the Prophets 116, Counts 117, Enjoyables 118 and Cavaliers 119 much harder. Though I understand the theory of the latter ones pretty much all being destroyed in the fire at Waxy Maxy's you expect more to survive if 2,500 were pressed.
All adds to the mystique I guess