I think the 'triggers broom' concept is very unlikely. Crystals and crowns get replaced because they need replacing, hands and dials less so but it does happen. Case replacement is rare and so is movement replacement. The chances of getting a watch that's had the case and movement replaced is extremely slim in my opinion.
The core of a watch is the movement and case in my view. Movement parts often need replacing and sometimes this involves second-hand parts because that's the most expedient way forward.
Obviously, originality is a factor with old watches but I think folks get far too precious about crowns and glasses, these get replaced for a good reason and it's crazy to retain an original crown that won`t seal properly simply because it's original. Ideally, an old crown can be salvaged by replacing the seal (I`ve just done one today), but that doesn`t usually happen.