We have to understand or consider that not all pictures posted and shared are of the final look. Often very helpful to show an area or process in steps
but of course the reference could be related to what order the layers were applied. Nice thing is that you can't tell in that area, if well covered with paint, the order below
Yes the original spray sound deadener and some sealers (not all) has something, likely illegal today, that could discolor light colored cars over the years Especially whites. Sort this did not look that way on a new car
I purchased some spray sound deadener for the first car I did for someone else - long ago. Showed up in a recycled milk jug, was water based, had sand in it and it discolored the white within weeks. Look very original but as mentioned in retrospec likely not like day one. Never could buy the stuff again. Someone likely caught the guy making it in bath tubs in his backyard