I have no reference source(s) for the info I am about to provide; most of it is based on articles I have read, the Glocks I own or have owned, and many other Glocks I have seen come and go through local gunshops and gun shows.
First, I have to confirm that the mag with the straight-tailed number "9" is also the same mag in the inset photo with the rectangular cutout on the front of the mag body. I assume you held the mags together, took the first photo, then rotated the mags without changing their relative position, then took the second photo. That would mean the two mags closest together in the composite photo are the same mag, and the two mags shown on the outer edges of the photo are the other mag. Is this correct?
If so, then the mag that has the straight-tailed number "9", narrow rear notch, and the rectangular cutout on the front is the type of magazine that came in the late 2000s Gen3 G26 (maybe as late as 2010?), just before the Gen4 guns and mags were released. It is not a Gen4 mag, because it does not have the third mag catch notch on the mag body. The rectangular notch on the front edge of the body is for a full-time ambidextrous magazine release (similar to the dual-button release on the G21SF models), and this style mag release was never used on small-frame (9mm/.40/.357) Glocks sold in the U.S. (as far as I know). I have two Gen4 mags that are very similar to it, differing only in having the third notch. Comparing the mags you have, it is the "newest" mag of the two.
The other mag looks like a slightly earlier mid-to-late-2000s Gen3 G26 mag. I do not have any single-notch mags with the high-on-the-mag-body caliber marking (signifying it was probably made after the AWB began); if it was any older than 1994, the caliber marking would be lower on the mag body. The mag body could have been made any time after 1994, but the follower number is the same as the other, newer mag, so it must have been fairly late in the single-notch-body series, just prior to adding the second rectangular notch, OR, someone has upgraded an older mag by adding a new current-issue follower.
The tapered appearance you talk about is a change made to all the small-frame Glock mags which I first noticed about 3-4 years ago. It does away with the ridge on each side of the mag that ran parallel to the feed lips, front to back, about a half-inch below the feed lips. It seems to make the sides of the mag smoother, and therefore less likely to catch or bind in the magazine well during a speedy reload, and I assume that is at least a partial reason why the change was made.
Last edited by DJ Niner; 10-07-2012 at 22:47..