I have every issue of “Cartridges of the World,” but could find no article specifically on Velet or Velex. Admittedly, I did not leaf thru each page of each edition, and they have a mediocre table of contents and a very poor index (in fact one issue seems to have no idex and after that one, the index is on of the cases types covered, not of any articles).
In “Manual of Pistol and Revolver Cartridges” (Handbuch der Pistolen- und Revolver-patronen), the combined edition, by Hans Erlmeier (shamefully not credited in this edition) and Jakob Brandt, there is a blurb on pages 642 and 643 about Velex, Velet (the name change) and Exammo.
I have nothing else comprehensive in my files - no actual articles at all.
Possibly one appeared in Gun Digest, of which I also have every issue, but no time right at the moment to go thru them all. If no one else answers this, I will try them when I have a chance.