Assuming your are in the United states a general guide is:

94 through 96 800 series offered the normally aspirated engine and

turbo models (2 engines). GLTs had the normally aspirated engines

during this time. Turbos came on Turbo or R models. The R

models could run extra boost for about 10 seconds so they have

more power (for 10 seconds) but I would not call them a 3rd

engine type.

In 1997 the light pressure turbo was introduced on the GLT in U.S.

and has been on all GLTs here since. So, now there are 3 engines:

base normally aspirated, light pressure turbo in GLT, high

pressure turbo (and 98 V70 AWD R with a bit more then the high

pressure turbo but still not a 4th engine type).

The light pressure turbo can also be found on some C70s and the

V70 XC models.

An 850 with a Light Pressure Turbo may exist in Canada or European

markets (but they also can have some combinations of diesel, 2.0 liter

engines, 2.0 liter high pressure turbo, and 10 valve

engines, 2.4, 2.4T, 2.3T, etc. in other parts of the world). I

believe A LPT is available on an AWD 850, too, in non-U.S. markets

(850 AWD never sold in U.S.).

Transmissions also changed a bit with a 5 speed automatic in 99 on

the normally aspirated models. 00's and higher all get it.

Variable valve timing also introduced starting in 99 along with

drive by wire (electronic) throttle.