Ryan, there is one really big difference and that's during construction, drywall is self supporting and plaster isn't. Plaster has to be supported ON something and that can be lath--thin slats of wood, or wire mesh. If you can find any way to see inside your walls, the difference is apparent. A quick way is to remove the cover plate from an electrical box-switch or plug. Look between the box and the wall and you will normally see one of these.
Another way to tell is if you are drilling holes to hang something up. With plaster, if you drill enough holes, you will hit some wood which will not have much depth/thickness or hit the metal lath. These will be somewhat apparent.
Drywall has a layer of paper over it before it's installed and you may find evidence of that under moldings or in the electric boxes.
While this is not surefire, plasters can mold corners easier than can be done with drywall. Plain wide arches can be either, but widely curved crowns with just a curve may tend to indicate plaster.
There are probably some other tips, but old time plasters could be pretty inventive in that era of relatively cheaper labor. Some of these would start with drywall and do plaster decorations over a thin layer of plaster on the old drywall. We have better materials for this today, but it seems to be done less often with higher labor costs.