You know, like how the Double Dare pilot was done by creator Geoffrey Darby himself? Maybe either Stone or Stanley did their own pilot before they collaborated with Nickelodeon, or something like that. I think that Legends could even be derived from an earlier Stone Stanley Production, Fun House. I don't think the pilot had to do with Nickelodeon, and even if it did, it was probably too crude to show. Game show pilots aren't like sitcom pilots: they use extremely simplistic sets, and especially with such a complex set design like Legends', it would be far too unprofessional to be aired as a regular episode.
Back to Blackbeard, I really now don't think that it would be a pilot or some sort, let alone the first episode of regular production. Think about it: it shares temple game props and a Moat crossing with the other four episodes taped completely in S1L5, and of course temple layout.
TMH, could you clarify what you mean by your last statement? Do you mean Blackbeard or Belshazzar, because I know for a fact that if it was Blackbeard, then why were the soapy slope, the peanut-filled shaft, and the pulley-pole were all used later in the other S1L5 episodes?