'Thanksgiving' is slowly forming offsets, but it has a way to go to be considered a clump. It is probably a form of the one-spot populations of Galanthus elwesii called monostictus.
The other early winter blooming snowdrop here is the one I call 'Christmas'. This is a two-spot Galanthus elwesii. I was looking at it today and it is already in full leaf and has formed a nice clump. But it shows no sign of bloom yet.