Please could someone help ID this Mammillaria, purchased unnamed from a garden centre this spring

Sorry for duplicate, but an improvement on last attempt.

I have looked at pics, seen similarities with canelensis, or marksiana, but there seem to be several species sinilar.

I have had the suggestion of Mammillaria johnstonii. Can anyone confirm?

I certainly could be M. johnstonii, with its central curling back towards the apex. However, there are several species that have this character, including various forms of M. wagneriana and pettersonii. I would rather wait until the plant has flowers before deciding, as the shape and colour of them would help a lot.
Sorry not to be more certain, and also for having missed your original post.

Thank you. I hope for a ring of flowers in 2017 to help decide the matter!