TG16 also wasn't "the 3RD system" of that generation either...I believe it came out around the same time as the Genisis. It's a lil' known fact that Nintendo was considering working with NEC to bring games to TG16 as opposed to making the Super Famicom. TG16 was already an established console in Japan & the U.S. versus the Genisis, so it was being considered before Nintendo just decided to make thier own system.
That generation also beheld the NeO*GeO as well as Pioneer's little known forray into video games later on. It was a modual system that played CD's, VCD's, full-sized LD's, Sega CD's, Turbo Duo CD's and eventually NeO*GeO CD's...not too many people know about it 'cos it was mega expensive (like over $1000) *and* you had to buy $100 to $200 moduals in order to play a different system. You plugged the modual in, it had controller ports & a "key" that told the Pioneer system to play games from whatever respective system was plugged in.
Stuff like this would eventually begot failures & failed ventures like Jaguar, Saturn, Panasonic REAL 3D0, CDi and of course Sony & Nintendo's "partnership" that eventually became the PlayStation. It's no wonder Nintendo was hasty to get into CD-ROM gaming as every system that did...failed. This, amoung other reasons would play a part in the exchange of crowns from Nintendo to Sony.
Oh yeah, I bought Bonk!
PS- I didn't mean to be condecending in correcting you, really it could be argued whether NeO*GeO or TG16 was "third" in that generation depending on who you talked to.