Ralf, your polythele is gorgeous and your obconella is really beautiful, Chris.
Nice photos!
I really have to rethink my polythele's.
What I thought was M p polythele now seems to be more the obconella as you described above:

Here is what was labelled obconella and probably now M p polythele:

Just for the record, here is the "nudum" which I now understand is an inermis form of polythele. How would one write that? Mammillaria polythele "nudum"?

These photos are a whole growing season ago - the plants are larger now - do they seem etiolated? They are on an east facing covered porch and get about 1 hour of very early direct sun.
Thanks again!
Shmuel