So I had a random thought yesterday. Where does the "4" come from in TI-99/4A? I know:
TI = Texas Instruments
99 = reference to the TMS9900 CPU in the computer
4 = ?
A = reference to the 9918A VDP used in the "4A" to distinguish it from the "99/4" which used the 9918 (no "A") VDP.
I can't come up with anything for the "4"... This has probably been discussed before, so obviously I did not do any searching before posting.