Absolutely
Before GT4, they did indeed record a lot of cars parked up. Some were also recorded on dynos and / or on track, there are videos of this on YouTube.
By GT4, they were supposed to be recording every car in the full range of operating conditions. The only issue is that they haven't incorporated that work into the in-game sounds yet, as it's all still the same format (schematically) used in GT2, except the separated and now directional sources (engine and exhaust). This is what the update will do, presumably.
The lack of Vtec crossover is because PD still only use three samples per source in the rev range (GT2 style): idle, low speed and high speed, with no throttle position variation. (Aside from the Red Bull X-cars, the Hudson is the only car I know of that contravenes this: it uses a sample almost every 1000 rpm or so, but still no intake.) With only two (non-idle) samples to play with, it would be possible to get that transition at the cost of some extra lifelessness in the rest of the rev-range. That still requires being aware of the phenomenon in the first place - it was something that all games struggled with for a while, strangely (sound artists just following a set recipe for all cars, I guess.)
The biggest change from Vtec crossover is in the intake anyway, so it wouldn't really make much difference in GT!