I have the original TI-89 that came out in late 1998- early 1999.
The original TI-92 which came out in the mid 90s was the first calculator that was capable of performing symbolic calculations (algebraic manipulations, symbolic differentiation/ integration, homogeneous first and second order differential equations…) as opposed to numeric approximations (like the TI-80 through TI-86). The TI-92 was not allowed to be used on many standardized exams (like the SATs) and many professors did not allow their usage in class since the QWERTY keyboard gave it more of a computer status than that of a calculator.
When the TI-89 came out TI released the TI-92 PLUS which looked like the TI-92 but had the same software as the TI-89.
TI skipped from TI-86 to TI-89 because at that time they claimed that the TI-89 would be the last calculator released in the TI-8X series since it has the capability of upgrading the software and downloading programs.
I lost touch with graphing calculators a few years ago (although I still have mine and use them from time to time). I think the version that I have has been discontinued for the TI-89 Titanium and TI added the TI-84 to the TI-8X family although I’m not sure what they do better/different than the rest of the family.
Oy, there’s so much more to write about graphing calculators.
Maybe later.