There's also another factor: you may not have any idea whose rebranded
switch you're getting when you buy a Dell switch. Maybe it's Foundry in
batch X, but it might not be in batch Y.
Is there any evidence that this happens within a model? I find it
hard to believe. I can see differences from one model to the next,
but from one batch to the next? When they went from the 5224 to the
5324, I believe that was a mfr changeout, but it was accompanied by
a new model number.
I hear your paranoia though. 
By the way, I know that for a while, Foundry wasn't building their
own low-end switches, which was how that Foundry 24G model came to
be... are they still doing that, or did they start making their own
gear again? I've had some old FWS24's for maybe 15 years and the
one thing I can say is that the stuff just doesn't seem to fail, even
though I don't really have a good use for them anymore.
... JG