The new one...

New acquisition, looks familiar but... Globose, flattened body, about 30 radials, 2 centrals - upper short almost invisible, lower hooked and hook pointing downwards. Centrals nice red/brown. Pot 6x6cm.

Hi,
Giving names to plants in the Stylothelae I also find challenging, and like you, I felt that I recognised this, so did some digging.
It reminded me of one that I had under the name of paradensis, and also of one called vergelensis. Some long time ago, we discussed this on this forum and one of the plants looks quite similar to yours. The thread of the discussion then is at https://mammillaria.forumotion.net/t120-mammillaria-vergelensis-n-n
So depending on whether you separate nana and duwei, your plant is related to them, I think.

Thank's, your picture of Mamm. paradensis looks very close. We'll wait for the spring and hopefully flowers and then have more material for conclusions. I also suspect on crinita/nana family.