Are 1991 348 ts clear coated?
Of course there is a clear coat! Its not the same ''color coat/clear coat'' type of system used since mid-late 90's, but there is clear on there! They dont spend hours color-sanding an entire car at the factory, so they shoot at least 2 coats of clear. in 1991, the urethane paints were barely known and not yet used in production cars... some types of urethane dont need a clear coat to appear ''glossy''. By the appearence, i'm pretty sure the factory used an enamel paint on pretty much all cars up to the 355 with a solid color. Sounds to me like part, or maybe all of your car may have been repainted with good 'ol lacquer... and probably only 1 coat of clear.
Been there, done that, got the T-shirt. My '94 was in such an abysmal state that I finally decided to have the whole car repainted. A previous owner had had partial stone chip resprays done and those areas were ok. The worst areas by far were the Ferrari original paint and the single most evident problem was the flaking off of the clear coat. Disgraceful really.