They did indeed diagnose Sarah shortly after T2 and said she had 6 months to live. John Connor states that she dragged it out the three years it took to get over the hump of JD.
To me that suggests JD was 2000/2001 which is inline with traditional assumptions of Armageddon/Apocalypse 'visionaries' et al. Given you ARE working with a human factored element here and that research could surge and lag on the chief programmer's (sorry, I don't remember his name only his "I'm not pant, sure, pant, how much longer, pant-pant I can hold this..." line) ability to recover and reverse engineer bits of the broken chip.
It also makes sense given that John Connor doesn't really look like a teenager but nor is he really over the hump into young adulthood which would make the 1997-2003 stretch somewhat more believeable (19-20 years old).
AIM-120 AMRAAM was promised in 1984, pushed back to 1986 and didn't arrive, in a faulted form, until 1991. Basic engineering 'shove right, promise left' logic.
On a side note, I found the notion of nannites (sp.) controlling civillian automobiles (gear shifter/stick, wheel and pedals) to be non sensical, even assuming that they are a 'part' of the intelligent mimetic derivative T-1000 alloy that T-X uses for primary replicant sheathing. How do they see? How do they transmit back to the T-X? How do they integrate what must be continually varying quantities of foot-pound level pressures upon such spatially separated controls?
From that early in the film it was a long struggle to stay the course as much was downhill.
The T-X simply doesn't cut it using Arnolds mini-mountain-moves slowmo dynamic and thus her 'fixated stalk' seems lacking in the dynamic energy one would expect from a smaller, more advanced, Terminator.
Too many times victims got away, too many times, when she didn't burst-transfer that focus to _cross the gap_ of engagement battlespace. And even when she did run, she lacked the bounding-lope of ungulancy (sp.) that I would expect of a large hunting cat. Instead, they simply closed in on her running frame in normal camera view which of course made the background blur.
While some may argue that this is all relative to '1-2 tonne fighting machines' weight categories, I myself have large problems with that statement as well.
IIRR most online references put Arnie around 400 kilos or approximately 830lbs and even this would _severely_ strain both locomotor servos and suspension (knees etc.) units while flat of crippling the types movement rates and safe navigation in many terrain types (footprint weights and why trucks can't drive on deep sand but tanks can etc.).
Last but not least, both dramatically and for-rating, when T-X blew away that kid in his own foyeur after having shoved him helpless down on the ground, T3 lost a bunch of points and indeed three people (with an youngish adolescent in tow) left from the theater. Comparitively, T-800 was so lacking in lethality that he not only seemed pansy-PC, but outright tactically _stupid_ (the scene at the filling station and the cops outside the mausoleum etc. both were highrisk threat zones that should have been _dealt with_, preemptively).
Other problems abounded (the FX frankly sucked and the absent Termi music leadin was also sorely missed) but in general I had low expectations and so wasn't altogether disappointed. Here's hoping that T4 either won't come or WILL be about a Death Match styled confrontatio between machines and men, to the end.
Saberist.