Sanding marks, decals and clear coats

For the following stages, I have to make my mind about three things:
1 - are the Lotus 49 decals still worth something after 18 years of uncontroled storage conditions?
2 - is it possible to spray a clear coat over decals?
3 - are sanding marks visible under a clear coat?

I went back to the hood of the Europa and divided it in three areas: the upper left section was wet sanded with a 400 grit paper, the upper right section was wet sanded with a 3000 grit pad and the lower, main section hosts a useless decal from one of the sheets contained in the kit. The first picture shows those areas. The section which is at and angle with the test sections is irrelevant, so please draw no conclusion over its finish. The area sanded with the 3000 grit pad looks worse on the picture than in the flesh. The finish is actually like de-polished glass, and not as white-ish as the 400 grit sanded area. The decal was as easy to put into place as a new one and the adhesive was still efficient. Once dry the supposedly clear borders look white over green and the decal has a mate finish.






































I sprayed two mist coats of clear before a wet coat. Contrary to paint, clear dries much faster and I was able to do all this and manipulate the part in the same afternoon. I could go that far since the clear did not seem to alter the decal in any way. Pictures 2 and 3 show light reflection on the hood after a thorough polishing job (wax, then polish compound then wax again).
Before I polished the part, it was obvious that the 400 grit sanded area was still visible, contrary to the 3000 grit sanded one. After I polished it, the difference is much less obvious (see picture 4). However, depending on how light hits the part the sanding mark are still visible, even though the whitened finish has disappeared (picture 4 again, note the upper left edge of the reflection of the lamp). The decal is now blended with the rest of the hood. Its thickness is noticeable both with the eye and the fingers but it now has the same glossy look as the painted areas. It is now sandable too, which is great! The white-ish finish of the borders is nowhere to be seen anymore.

Well, now I have answers to my questions:
1- the original decals are still workable. However, used in their current state, they would make the model look aged and well past its original would-be appeal.
2- a clear coat has not affected the decal in this example. I dare say it should be the same with the other ones. I was half-expecting wrinkles or even some sort of dissolution, but no disaster happened.
3- deep sanding marks stay visible in spite of a clear coat. There is no alteration of the colour on the end product but scratches are visible under the gloss. It is thus better to pile on the sanding stages by using thiner and thiner grits before applying a finishing coat.
I would add that a clear coat allows for an even look, for a thourough polishing operation over decals and masks the little touch-ups done with 3000 grit pads. Which is a good thing since I had to use some after the final paint operation! However, it looks like a thick coat is needed in order to even the surface irregularities. By irregularities, I mean the thickness added by the decals, and also the edges of the colour application: there are 2 coats of yellow over the white colour on the body, and 4 coats of yellow and green.