My derm said that the yellowish color is (due to) lymph / lymph water (whatever you call it; I don't know if there is a difference between "lymph water" and pus/sanies). Now that I'm regularly washing my lips with qtips, the qtips get somewhat yellow as well and the lips / crusts are not as yellow anymore (but I don't let them get as thick as before anymore either, so I don't know how yellow they would get if the crusts got thicker).
I also think that having the very thick crusts on the lips can't be good. In my case, the crusts would separate from the lips on a few spots and water would get in from the sides. It would then stay there and start smelling after a while. So not a good environment to start healing really.
Healing2021, hopefully you'll have success with your wound theory. I myself don't really think it's a wound though. It's said that wounds heal better when being moist, but they usually don't stop healing completely while not being moist, do they? But still, good luck and let us know :)