" I found that enamel paints tend to be solvable basically forever by their thinner "

Uh , what ?

If we're talking about alkyd resin " enamels " , they cure thru oxygen absorption and become unsolvable by their thinner ( mineral spirits , turpentine ) .Extremely resistant to other solvents when fully cured .

Acrylics will dissolve in alcohols , the solvent when the paint is mixed , but obviously not the thinner - water .

Lacquers will also go back into solution with the same solvents , mostly acetone .

Enamel upon enamel is fine but wait a bit .( how long will vary with the brand and environment )  - or use an acrylic wash  ; no fumes and easy to remove with isopropyl alcohol if your base-coat is enamel since the isopropyl will have no effect on it .