I think that Volvo's procedure for automatic transmissions was to drain the pan and change the filter. This is a partial fluid change. I call it a slow fluid change.

On the 850 board, the new procedure for home mechanics is to do a slow fluid change - drop the fluid in the pan at every oil change until the fluid looks nice and clean.

I once had a full fluid flush by a dealer and in a week or so the fluid was a bit dirty. I complained and i was told that evidently the pan was not drained before the flush, so they did another proper flush.

If you change all the fluid drain the pan first off.

In my 60 years of working on my cars and talking to other owners, I have heard of several disasters when all the transmission fluid was changed. Even some stories on the 850 BB.