Americans from the seventies often had a thermoplastic lacquer layer. If those classics later got a new jacket there or here, it often happened quickly for cost reasons and with an 2K paint. And there the misery began.
Those paints do not tolerate each other. And that's not as often said because of something scary and chemical, but actually because they have different coefficients of expansion. This causes the underlying layer to 'draw' the top one.
The more serious painters soon realized that an insulation layer between the lacquer layers at least delayed that process for a long time. But in the meantime it has turned out that the people who told us that such a carriage, sprayed in thermoplastic paint, had to be sanded completely bare nevertheless got the same.
So if you think your car needs a new coat of paint, then the advice is: keep sanding until you are on the blank plate. This advice does not apply to Corvette owners.