I always thought that the Room of Harmonic Convergence was a deadend in "Magellan" also. I mean, wasn't there a small noise made when Robert tried all of the steps in that room? It would've just seemed like a harsh deadend to me. Even Kirk seemed convinced that it was not a deadend.
Do you mean to say that you always thought that the room WASN'T a dead end? 
Oops, I meant to say I always thought that
wasn't a deadend. Thanks for pointing that out.

Why should that matter? There were plenty of episodes from Season 2 and 3 where the number of rooms between the half pendant and the final temple guard (or what would have been the final temple guard, in the event that the team did not encounter the third guard) wasn't the same; why can't that be true for Season 1 as well?
Just to name a few for reference: "Crown of Queen Nzinga" was one room away; "The Bifocal Monocle of One Eyed Jack" would have had to have been at least two rooms away (the half pendant was picked up in the Tomb of the Headless Kings, and there are no temple guards in the Jester's Court); and "The Mummified Hand of the Egyptian King" would have been either three or four rooms away from the final temple guard (the half pendant was on the left-hand column in the Chamber of the Sacred Markers, and the number of rooms to get to the Secret Password depended on if the contestant would have had to go up to the King's Storeroom or directly to the Ancient Warriors from the Sacred Markers). Either way, there was much variation in the number of rooms between picking up the half pendant, the room with the second guard, and the room with the final guard.
Like I said in an earlier post, "As nice as that trend seems, we automatically know that it does not hold true for every episode."
I don't really compare the season one temple with the later two season temples. By season two, there was a different set of producers that made the temple. That is why in season two the half-pendants were made much more easier than season one probably. Also, the season two 1.5 pendant teams usually got banked on for having a half-pendant where the producers set the team up where it wasn't possible to avoid 2/3 of the guards. So whatever trend occurred in season two or three, I don't really compare with season one.
I am not saying that all the half-pendants had to be one room away. Look at "Pecos Bill's Lost Lariat", that proved that it wasn't always the case. And with your "Magellan" and "Jean Lafitte" pictures, its also possible those were the half-pendants after all and that the half-pendant wasn't always one room away. But alot of season one temple runs did have one room away half-pendants:
"Gordian Knot", "The Trojan Horseshoe", "King Tut's Cobra Staff", "Mata Hari", "Henry VIII's Great Seal", "Anne Bonny", etc. So it does kind of help narrowing it down. But yeah, it doesn't always mean that the half-pendant was one room away. But you have to admit that this pattern appears in a lot of season one runs.