I think as time has revealed more and more the true rarity of games the scale has adjusted accordingly. It by no means has stopped adjusting. A few games are known in terms of their very limited quantity as the programmers have been contacted and interviewed and have given a fairly reliable sense of the number of games that were produced. Others remain a mystery but likely the developers will be discovered and more info gained as time goes by. Ebay, like it or hate it, has revealed a truer rarity of many games, including Chuckwagon. There are members here who can answer this better than I can, but this is my two cents. I am convinced there are folks here who have stuff that only a very select few even know about, which is fine. It only makes collecting for the 2600 more fun. Someone here likely has a lone copy of something like Water Raid by Menavision, a Xante copy of E.T., or Video Death by Commavid. Hell, someone here may even have the real Holy Grail tucked away somewhere. At any rate, Air Raid seems to be the Big Sexy right now in terms of overall popularity but I am not convinced it is THE Holy Grail. I would like to see Eli's Ladder in its entirety (meaning overlay, charts, etc.) go on eBay and see how it would fare compared to a CIB Air Raid. And of course those you mentioned that are limited to one or two known copies would be interesting auctions as well.
Nice post