Copyright date surprise -- pilot episode?

Two days ago (September 24, 2013), I caught a few minutes near the end of THIS-TV's 5:30 am (eastern time) airing of Sea Hunt. I've confirmed from its cast list at the end, and from THIS's online schedule, that it was the episode "Mark of the Octopus", the 4th in IMDB's list. What surprised me was that in the end credits, the copyright date was (if I read it correctly) MCMLVI -- 1956! Perhaps someone with the DVDs can confirm this. If I'm right, I have to think that THIS is the series' pilot episode (rather than "Sixty Feet Below"), despite its being the fourth aired.

Now it's true that more often than not, the first-aired episode of a series is the pilot, but by no means is this ALWAYS the case. Ivan Tors's own Flipper is one exception -- its pilot was its third-aired episode, "S.O.S. Dolphin" (its first-aired episode paralleled Sea Hunt, in that it was titled "300 Feet Below"!). And the original Star Trek's pilot was also its third-aired ("Where No Man Has Gone Before"). The Bob Newhart Show's pilot was its ninth-aired. Lassie had two episodes shot as pilots -- the "first episode" (which it indeed was), "The Inheritance", and a "typical episode" (which pilots are often supposed to represent), "The Well", which didn't air until late in the first season. BTW, like was reported on these boards about Sea Hunt's pilot (stated as "Sixty Feet Below"), those Lassie pilots were originally filmed in color, but only aired in B&W -- though I'm wondering now if the Sea Hunt pilot was misidentified, merely stated because it was first-aired.

But I'm also wondering if there are additional Sea Hunt episodes dating back to 1956 -- I haven't seen if that's the case; perhaps, again, DVD owners can check on this -- maybe including "Sixty Feet Below", so perhaps it really IS the pilot after all? Is it possible that a number of episodes were produced more than a year before they made it to air? That's about what happened with the entire first season of The Adventures of Superman, also a syndicated series.

So I'm wondering if anyone can clear this up!