There is a thread here every few months about whether or not biscuits show
through. Most people say they have never seen it, but a few insist it
happens all the time.

I made up a game board out of 1/2" ply recessed in a frame of walnut. I cut
the biscuit slots off center so the thin side would be on the bottom.
Unfortunately I screwed up in cutting the slots on the mating pieces and the
spacing only worked with the plywood upside down, with the thin part on top.
Normally I would have redone it, but this was for a project my son was doing
for 6th grade and it didn't seem right to fuss too much over it; so I went
with what I had. (besides, I could blame it on my son!)

Well, they didn't show at first and they still don't show a week later. If
they don't telegraph through 1/16" of plywood it is hard to believe they
ever do. And yes, they are nice snug fits; PC 557 and PC biscuits.

I have read that European biscuits are compressed, but PC found that they
work the same without compression so PC biscuits are not compressed. Maybe
that accounts for people's varying experiences?