Okay, I've done some more in-depth research about the Ledges for Season Three. The only episodes where the lighting is dark in the Ledges during the temple overview (when Olmec is saying "The choices are yours, and yours alone..." all the way up until "Return through the gates with the artifact in three minutes, and you will both be handsomely rewarded, and here's how!") were:
Episode 84- The Much-Heralded Helmet of Sir Gawain
Episode 98- The Mysterious Manuscript of Mary Shelley
Episode 99- The Dried Apple Half of William Tell
Episode 103- The Lost Hornpipe of the Pirate Captain
Episode 117- The Jeweled Scabbard of Sforza
Episode 118- The Good-Luck Watch of Empress Eugenie
We know that there was a guard in the Ledges for "The Dried Apple Half of William Tell." In all of the other five episodes, only two or fewer of the guards were encountered: Gawain had none; Manuscript had Chamber and Shrine; Hornpipe had Chamber and Ancient Warriors; Scabbard had Crypt and Chamber; and Watch had Storeroom and Shrine. We have already discussed the Gawain and Scabbard episodes at length, and I believe we all agree that the Ledges probably contained guards for each of those episodes. Now I'd like to focus in on the Manuscript, Hornpipe, and Watch episodes. Each episode provides clues as to why the third guard was most likely stationed in the Ledges, one at a time. (And as always, photos used here are courtesy video from youtube.com posted by ChargerTheWolf.)
MANUSCRIPT:

The path consisted of the Crypt, Pit, Chamber (avoidable, but Kate took it anyway and encountered the first guard there), Storeroom, Ancient Warriors, and Shrine (second guard). The object was in the Dark Forest, so it is possible that the team would have had to have entered the Secret Password and/or the Quicksand Bog. I can't make any assumptions about the Room of the Secret Password, but it seems statistically improbable for the third guard to have been there. Even though the television viewer never gets a view of the entire Quicksand Bog, I have a screenshot of the largest portion of the room shown during the temple run. It seems like there should have been some Styrofoam blocks piled high enough to get captured within the camera's view if there were a guard in the Quicksand Bog.

HORNPIPE:

The path consisted of the Crypt, Pit, Tomb of the Headless Kings, Chamber (first guard), Storeroom, Ancient Warriors (second guard), Shrine, Secret Password, and finally the Quicksand Bog. Before I proceed, I just want to point out that the step in the staircase from the Pit to the Storeroom dropped upon knocking over the column, so the Pit/Storeroom door should have unlocked in addition to the Pit/Tomb door. In addition, when Jarrid is exiting the temple, the Pit/Storeroom door can be seen, and it still sealed shut. This implied that that door malfunctioned, and that Jessica and Jarrid could have used it, providing a shortcut that would have eliminated the need to pass through the Tomb and the Chamber. You can even see that Jarrid tried to use the Pit/Storeroom door upon entering the temple; that would have saved the team a whole lot of time. It probably would have also reduced the amount of admiration this particular run gets.
Okay, now that I've mentioned that, let's continue on to talk about the guards and the Ledges for this episode, shall we? Even though Jarrid was only in the Secret Password for a few seconds before he doubled back to the Shrine, the guards in the Secret Password have been noticeably prompt and speedy at coming out of that room in Season Three: just look at "Thornwood Gavel" and "The War Fan" episodes, for example (Don't give me any of that "Well, that was earlier in the season" shmaltz). The team entered every room, excluding the Jester's Court, Dark Forest, and the darkened Ledges. Neither the Tomb/Jester nor the Shrine/Forest doors opened, so the path could not have led them into either of those rooms. I think that eliminates all of the rooms besides the Ledges to house the last guard. And, conveniently, it is one of the few episodes where the Ledges are completely dark.
GOOD-LUCK WATCH

The path consisted of the Crypt, Pit, Storeroom (first guard), Ancient Warriors, Shrine (second guard), Dark Forest, Jester's Court, and finally the Tomb of the Headless Kings. Only the Chamber, Secret Password, Quicksand Bog, and Ledges were left unentered. The Pit/Chamber door, the Shrine/Password door, and the Shrine/Bog doors did not open after each of the respective room objectives was completed. In other words, the Chamber, Secret Password, and Quicksand Bog were not to be entered for this run, and therefore should not have housed temple guards. The only other room left unentered was the Ledges. This means that the team traversed through every room that they could have in their path, except the Ledges. That means that the Ledges, therefore, should have housed the third guard for the "Good-Luck Watch" episode. And once again, it is dark in the Ledges during the temple overview.
I am very sorry that this post is so long, but I really, truly believe, that the lack of light in those particular episodes is very suspicious. Those select episodes are the only ones of the entire third season to have the Ledges dark like that. Moreover, the episodes are not all from the same production day. And each of these episodes has clear evidence, which I have stated above, to support the idea that the unencountered temple guards were in the Ledges.