It's a physical device at the bleeding edge of capabilities. Defects are pretty much a guarantee, and getting a working sample is a numbers game. Is it really that strange to not get a 100% yield?
Having 5 working devices out of 21 is normal. The problem is that the other 16 weren't mentioned.
Well you also need to account for what kind of deviation are we talking about between the 21. If they selected the 5 because they were the best, but the others showed results that were within say 0-5% of the 5, then sure that is acceptable. But if we’re talking about flipping a coin 21 times, seeing heads 16 times and then choosing the 5 tails outcomes as the results, then I would say that’s pretty unacceptable.
I do not think this is the right metaphor. Having 5 devices work out of 21 is actually a better yield than what TSMC would get with a brand new process. This is not just normal, this is expected. It is all the other allegations that make this be a very questionable case.
Like I said, a single misplaced atom is enough to wreak havoc in the behaviour of these things. That's not the problem, everyone knows there's a large gap between phenomena observed, and making it consistently manufacturable with high yield.
Having 5 working devices out of 21 is normal. The problem is that the other 16 weren't mentioned.