silvering of the smaller stencils

Something you could try (I haven't, but it might work) is insinuating Future under the decal. Put a small puddle of Future over the decal, and try to work it under by probing the edges and pressing down with a small, stiff, brush.

Well, if you've overcoated the decal with anything, that's it. You can try one of the stronger decal solvents, like Solvaset, and use a small paintbrush to try and work the solvent around and under the edges of the little guys. That may, or may not, encourage them to stick down.

I've experienced the same problem with many small stencil decals, no matter how careful the preperation & application.  I think it's caused by the small area being covered by the decal & possibly not enough decal adhesive being transferred by the small decal.  These days, I test the stencils first in a low visibility area & if it shows signs of silvering I remove it & don't proceed with the rest.  I'd rather have a build without stencils than a build with silvered stencils.  As far as fixing it, others may suggest techniques, but personally I've never found a method that works consistently or reliably.

Regards,  Rick