Heat will remove the decals (even with paint over them, provided the PO didn't use rhinoliner). Then there's the 30 year old adhesive.
I'm no chemical engineer, but I can tell you the adhesive definitely changes the paint under it. When I had my truck repainted the guy stripped
the decals and prepped those areas before shooting the primer.
'88 Pioneer decals removed, you can see that where they were, required special prep as well as more sanding.