A North American native sedum - Allegheny "somethingorother"

A couple of years ago a client in Ontario asked for some native succulents, in particular native sedum species plants for their green roof. I know of very few in Ontario, almost none grown commercially. I did some investigating, a lot actually, about indigenous sedums and the easiest one to get was Allegheny somethingorother. I say that because there's a debate as to what it is actually called.  
I've seen it called Allegheny Spurge Sedum (a.k.a. Pachysandra procumbens) and also called Allegheny Stonecrop (a.k.a Hylotelephium telephioides). How can the same plant be called two different things? I have no clue.
There's another funny bit on the Wikipedia page...that the plant has "introduced" itself into Ontario (when?). That leads to a bigger question, does that make it native? 

I'm comfortable just calling it a successful North American native (it seems good from possibly USDA zone 8 to zone 5) and observing it carefully in New York and Ontario, where I have some specimens planted.
After a year, so far so good. Here's a few pictures of the plant. It seems to grow ok from cuttings.