If you consider that a door trim panel starts as a plain piece of backing board, to which the upper fiberglass "curve" is stapled to, then the trim items are added to, it is all "built". ONLY issue is that the vinyl trim usually is heat-pressed to shape and contours, not sewn. THAT is the main issue, to me. Bad thing is that, even with expertly-done things, it can easily look "cheaply-done" if it is not done as the originals are done. If there is an accent trim section that can be done separately from the main covering, as some were known to do back then, then re-doing just that one piece might be doable, IF done as closely as possible to the OEM item.
In cases where larger plastic pieces have started to craze and disintegrate, sometimes they can be sanded smooth and recovered with a stretchable vinyl fabric with approx the same grain pattern. Or some properly-serged edge automotive carpet applied to them.
Of course, what is done to one panel needs to also be done to the rest of them and the B- and C-pillar plastic items, too.
Just some thoughts,
CBODY67
