There is one VT or VT0 model parameter.
There are several "VT"s you can measure, or calculate,
from device I-V curves and you may see more than one
in a WAT report. VTlin, VTsat, ... differ by measurement
conditions and possibly regression method (and, in some
cases, a simple VT(1uA) uses no figuring at all, just force
and measure).
30 years in this game, 15 of it mostly-CMOS, and I'd have
to look it up myself - because it's not really important
enough to have remembered. If, in fact, it was even
significant enough to have been taught.
Professors delight in passing on pedantic and not-
especially-useful distinctions; they just have to fill a
semester, with something.