Unless something has slipped by me, all 41 magazines have a removable floorplate. The newer ones have a blind hole, but the floorplate still comes off.
The major difference in the mags is the follower. The older steel follower is esteemed by some, although the black plastic works as well for me. I am not totally happy with the red plastic 12 rd follower, but some seem to like them as well.
The old two piece tube that smithfan refers to functions the same as the new ones, no better no worse. I have one in my regular rotation. The SIG fans would call them a “railroad magazine” they look vaguely like railroad tracks from the back.

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