any unfalsifiable assertion is worthless trash and isn't a path to knowledge unless you really want to undermine the entire concept of knowing things. not sure how one would simultaneously claim to know stuff and that knowledge can't hold certainty.

note that we don't strictly need to be able or particularly likely to find or demonstrate the counter-evidence. Evolutionary biology would have to be reevaluated if modern rabbit fossils were found in the precambrian sediment layers, but rabbits are small so we could go a while simply not finding them.