Could they be seedlings that have grown?

Definitely not mxk3 z5b_MI they are sterile. For some reason they arnt as tall as they used to be either. They were a good 5 ft tall last year now 3 ft. Very strange. Only thing different is my crabapple tree fell over last year which did shade them a little.

I don't think one can ever be positive a plant is sterile; odds are it is if bred to be so, but I don't think there are any guarantees.

I bought 6 and have had 6 for years plus I know for sure they came back from same plant because I cut old stems in spring when new growth starts on them. I wish they did reseed.