I've been building since the early 60s and I noticed most model enamel bottle paint formulas changed somewhere in the 90s. For whatever reason or whatever was changed they seem less effective. I find them today to be thinner, more translucent, dry stickier or more slowly, don't cover that well and the flats are not so flat as they once were. Kind of like there's less pigment in the mix.
The good old days