I am actively trying to track down old sellsheets, press releases, and catalogs so I can nail down some more of the early history of BattleTech myself. The problem is that the mid-80s saw an explosion of new games and BattleTech was very much one (initially) tiny property among many, so a lot of that trace evidence is long-gone or in the hands of people who are disinclined to share it.
First real 'golden age' of gaming was the mid eighties, wasn't it? ISTR that RPG's and tabletop were in the news and I actually think a lot of it was the 'satanic panic' and teevee movies like "Mazes and Monsters" that drove up interest in the hobby.
Kind of the way the PMRC sold records in the same timeframe.
First ad I ever saw for Battletech wasn't even for Battletech, and it was in the back of an issue of Marvel's
Star Wars comic. Had a static image of a WHM-6R, and named some of the iconic first generation 'mechs by name (I can't recall all of it, I was a KID...)
I can't remember the NAME of the first fiction I saw for Battletech, but it was a short story-but that's a couple three years AFTER Decision at Thunder Rift came out...and it was probably something that would qualify as "Fan Fiction" anyway.