I finally received the first 10-round magazines for my M&P9c today. I ordered them from Smith & Wesson about a month ago. I had to take delivery of my M&P9c without magazines, because it came with 12-round ones. I live in California.
Anyway, the magazine body of the 10-round magazines for the M&P9 and M&P9c is the same. They differ only in their floorplate and spring. Interestingly, the same is not true of 10-round M&P40 (M&P357) and M&P40c (M&P357c) magazines.
Also, the M&P9c 10-round magazines are easily differentiated when the magazine is in the pistol. I need to take photos to illustrate.

Anyway, the magazine body of the 10-round magazines for the M&P9 and M&P9c is the same. They differ only in their floorplate and spring. Interestingly, the same is not true of 10-round M&P40 (M&P357) and M&P40c (M&P357c) magazines.
Also, the M&P9c 10-round magazines are easily differentiated when the magazine is in the pistol. I need to take photos to illustrate.