The fact that, prior to Lew, Smith and Wesson never offered a 3" .44. What Horton does is order special runs of pistols in configurations that S&W doesn't offer. My LH 24-3 was from, I think, 1983. The "FBI Model" of the 27 (the 3.5" bbl) was a very popular pistol configuration, but the 27 was the only N frame ever offered with a bbl shorter than 4" from the factory. Some liked the pistol, but didn't care for the .357 chambering.
I believe they are just special run line guns, but every Horton I have shot, seems as if it is just a little tighter/smoother than a regular production piece, but that could just be in the mind.
The best way to tell if a piece you are looking at is a real LH offering is to do your research with Supica & Nahas "Standard Catalog of Smith and Wesson" and the Blue Book.