The Genesis launch line-up isn't solid either unless you're talking about a window of time.
The Genesis launch lineup is pretty much set in stone as far as I'm concerned. There is a VERY convincing USA Today newspaper article from August of 1989 that features children playing the full batch of launch games for the Sega Genesis. You combine that with more evidence from usenet posts of the time, and it's pretty much about as confirmed as you can get, without having a time machine and recording videos of the whole thing.
USA TODAY Article from August of 1989:
http://i27.photobucket.com/albums/c186/sanpojin/USAToday2.jpghttp://i27.photobucket.com/albums/c186/sanpojin/USAToday3.jpgUsenet post thread:
http://www.sega-16.com/forum/showthread.php?6513-Usenet-guy-reviews-the-quot-Sega-Genesis-quot-%28August-1989%29These two pieces of information, pretty much confirms that there were 6 games launched for the Genesis on August 14th, 1989 (New York & Los Angeles areas)
1. Altered Beast - pack in
2. Tommy Lasorda Baseball
3. Last Battle
4. Space Harrier II
5. Super Thunderblade
6. Thunder Force II
There are a number of other sources, that help confirm this information, but I'd have to look through my notes to find all of the particular info. Bottom line, I feel really, really good about the Genesis launch list.
When it comes to the TG-16 however, I'm starting at square one. I've search usenet repeatedly looking for any mentions of TurboGrafx in August and September and October of 1989, and there just aren't that many posts about it. No conclusive list as far as I can remember.
Also, I don't know of any USA Today article regarding the TG-16 or early store advertisement scans or anything like that. I have most of the video game magazines sold during that time period, but magazines are very, very unreliable with their dates and lists. In fact, I've found that magazines more often than not give mis-information . Sometimes in the letters section, and the tips and tricks section, you can get valuable clues as to when something was released, but for the most part, I don't think magazines provide very compelling evidence. Usenet posts are probably the most valuable information, because it's time stamped. Newspaper articles are also quite valuable, if you know the exact date of the newspaper. It's also time stamped in a way.
That USA Today article that I linked to, we don't have an exact date for that. Supposedly it is sometime in August of 1989. There might be a way to use USA Today archives, to trace the exact date of that article, but you probably have to pay some kind of fee to access their archives. I've thought about searching the microfilm of my local newspaper, to see if there were any articles in the business section around the time of release, or maybe Toys R Us or Montgomery Wards ads or something...