Thanks for the information Len. I now know of three "Haenel Air Pistols" with the small flanges, so it is looking like a diagnostic. It would be nice to hear about a few more though.
As I indicated previously. it would be equally useful to know of any "Haenel 28's" that might exceptionally have these small flanges. The lack of response so far, given that there must be many "28" owners reading this thread suggests that there may not be any, and so the change was sharp with no carry over.
The rod shaped latch, as opposed to the hook, is very characteristic of the "Haenel Air Pistol", but I did have some verbal information a while ago (unsubstantiated) that some of early 28's many also have had this. If anyone owns a 28 with the rod latch I would love to hear about it.