I believe when they first became available they were advertised as having 15 round mags but people were reportedly getting 17 rounds in the 15 round mags with a small amount of folks reporting failures related to forcing the 2 extra rounds in. But now, as far as I know, they’re all sold with magazines that are actually stamped with 17 round indicators on them.
I actually have a CM9 Gen2 that came with the 17 round stamped mags. The MecGar 16,17 & 19 round mags function fine in it too.