Unfortunately if the precise construction of said structures is known, it becomes vulnerable to specially crafted radar pulses which make it generate strong returns.

So it's paramount that the exact layout be kept secret (and likely there's some variation between manufacturing batches, but this is just conjecture).

Needless to say, the US very likely has this info on every jet it sold, and a sufficiently motivated and sophisticated adversary can likely figure this out if the plane spends a long enough time in front of their radars.

That's why the US has been extremely careful about where and how the F-35 gets to fly.