Blurry- Sorry, but I think that amounts to playing wordgames. Those who believe BF, IF it is" real", to be an animal, offer no such" unverifiable" claims. They expect BF to leave tracks (and believe we have such tracks- see Krantz, Meldrum, etc), and other physical traces. They believe folks should- and do- see BF. They believe BF should be photographable, etc. In other words, they fully expect BF to be as verifiable as any other (rare, elusive, possibly very intelligent) animal would be. These expectations are in direct contradiction to what Sagan was discussing.
When pressed to explain why we don't have MORE such evidence, right now, they may indeed offer speculations as to BF's possible rarity, etc. But on the central, key, relevant question- is BF a living, breathing, tangible animal- I respectfully suggest there are no unverifiable claims being made.