Now I dont have every type of board/cap (yet

but all my key caps that have shine after real use (i.e more than a few weeks).
The shine comes from the surface of the cap getting worn.
This seems to be the case (IMO) even more with Filco caps, there was the same problem with the Das IIRC.
I got shot of my Das within 10~12 weeks and that had shine/ware on the caps.
If you can show me how to "clean off the shine" than I will put my hands up and say sorry.
But IMO shine on caps means the surface has worn, might not be much, but worn none the less.
If not, I have 5 brand new sets of Cherry 2shots that are used, but just need a clean to make them brand new again.