...but you don't seem to apply this logic to fiat currencies. It seems that by definition, any time they are replaced, it is because they have failed.
That's not what I said.
Well it is exactly what you said. You said that 100% of fiat currencies have failed:
Fiat currencies have a 100% failure rate
I guess my succinct catch phrase stands corrected. So, instead "100% of fiat currencies fail or get destroyed." Hope that's better.