Stan has pretty much id'd our plant as most likely a Citrandarin or possibly a seedling from it (maybe Changsha background), through information that was collected by my friend Dave K. tracing back where he bought the plant and when. That makes complete sense given its hardiness, flavor, etc.
We're going to start grafting it on Poncirus stock to increase our tree in spring just to be sure we at least have a few more clones.
We'll continue to grow out our 18 or so seedlings too, and document the process carefully.
Thanks Stan and Dave!
Boca Joe, an amateur but learning fast B-)