Just catching up with this one Geo, and it's looking good.
That 'mottle' pattern on the decal sheet looks like the effect of either a tissue cover sheet, or perhaps a cellophane or poly bag, being in close contact with the surface, It's a fairly common effect, even with the often used tissue sheets used as protection, when the latter sometimes lightly adheres to the surface, and 'sweats' slightly, causing a minor reaction with the sealing varnish.
I've even seen it where the tissue has actually stuck to the surface of the decal sheet, mainly on old decals, and left behind small patches of tissue or fibers when peeled off. But in the majority of these extreme cases, the decals themselves have not been affected, as the tissue dissolves and floats off the surface when the decal is immersed in water.
The mottle is normally nothing to worry about, and is just a non-permanent, patchy dulling of the gloss finish coat. However, for future reference, if in doubt, inspect the decals closely for visible damage, such as abrasion or cracking, and give them a coat of clear acrylic varnish (NOT 'Future', as this will dissolve when immersed !). This is something I do with all older decals I may need to use, and any I may have doubts about - particularly 'Microscale / Superscale' decals, the majority of which could date back to the 1970's or 1980's, even if purchased as new recently. Some of these, especially the smaller items and stencils, have an annoying habit of breaking up, deforming, and even dissolving when immersed !