What I meant, I guess is that they probably aren't a quad manufacturing plant, that has a big investment in all that goes into making quads, with a big storehouse full of spares... They are probably a small shop who comes up with a design and farm out the pieces to various suppliers for manufacturing. They produce something that is largely disposable and it hardly matters if the next one is identical to the last one. They probably do production in batches. (So once a run is done, it's done). The cost in changing a board design is in the design itself. It's not like automobile manufacturing where there is huge investment in tooling. So between runs someone was trying to figure out how to make the next batch with a better profit margin and the whipped up a new design. Or the supply of one of the components dried up which forced a redesign.
The point being is that there are tons of good reasons why the board was changed. And about zero reasons to expect that we'll see new stock with the old generation of boards (unless it gets cloned and shows up somewhere else).