Specifically the Atari 2600. My collection stemmed, like a lot of peoples collections, from things from my childhood. The one difference here is I was collecting for this particular system while they were still making some games for it. To give you a time frame, the Nintendo Entertainment System was out in full force, Atari (as people knew it) was spiraling down with failed system after failed system. I bought brand new games in the clearance bins for little more than a dollar. Then the Super Nintendo came out, and Atari 2600 games found their second life at garage sales and flea markets.
I remember seeing boxes and boxes of Atari 2600 games littered across many flea market stands. I would comb for hours sometimes through hundreds of cartridges and accessories that I didn't have. The going rate for games in the early 90's... $0.25 to $1.00, yep. I would pass on a stand if they were selling them for over $2, they just weren't worth it. And this is well before even knowledgeable Atari 2600 players or the Atari Age website even started.
I shudder to think the rare, or even prototype games I might have passed on because they were asking $3 or more for a game. Hell loose NES games were going for $10 and that system was still relevant at the time. I don't have too many boxes for the games as the games I bought new off the shelf, well at the time when the system was still relevant, why would you keep the boxes? It was the game and the manual that had any sort of value. Boxes just took up room. Hind sight is always 20/20.
I doubt I saw a T-handle Air Raid cartridge in those years, but it could be possible that I passed it over thinking it was for another system, doh!
Since the "internet age" began my collecting became more casual. I only buy or collect a game or peripheral that I really intend to play with. I never had the intention (even back then) to be a completionist or collect a "super rare" game just because it is "super rare".
I also own a Panasonic 3DO, now there is a flop.