The limit does not exist. Not theoretically. The deaths of all the Time Lords before, were told by the 3 founders that they only had 12 regenerations, to protect the founders' power. This is how Ruth fits in between or before the established 13 Doctors. And why the Doctor doesn't remember.
- Spoilers for "The Timeless Children": Sort of Confirmed. The limit was decreed by the Time Lords, and doesn't apply to the Doctor since she isn't native Gallifreyan. Ruth is also Confirmed to be a pre-Hartnell Doctor.
We know that Rassilon and Omega existed, and Omega had no reason to lie in "The Three Doctors" about attempting to tame a black hole. But Omega fell into another dimension, and Rassilon instead used knowledge from the Cyberium to turn the Gallifreyans into the Time Lords (possibly referring to it as validium, and leading to the Seventh Doctor foiling the Cybermen's attempt to recover it in "Silver Nemesis" without realizing the full extent of what was at stake).
- Jossed. Rassilon and Omega existed (we've seen them on screen) but weren't the founders. The Cybermen were drawn into the story by the Master, and have nothing to do with Gallifrey.
Ko Sharmus says that Gallifrey looks different through the Boundary. That's because, before the Master redirected it to make his entrance, the Boundary led to Gallifrey in the Old Time — that's where the humans who previously escaped the Cybermen fled. Having traveled through time such a long way, those humans are suffused with artron energy (note the reminder of that earlier this season) and the Time Lords use them as a power source (the "Timeless Children").
The only thing wrong with this theory is that the Master is so horrified by this that he destroys Gallifrey, when honestly the whole thing sounds a lot like one of his own plans (even as recently as "Spyfall"). The idea of abusing future humanity to create a Time Lord-like society is pretty much exactly what he did in "The Sound of Drums"/"Last of the Time Lords," so it shouldn't be Even Evil Has Standards either. Maybe he destroyed the planet because he felt they were ripping off Saxon-Master's plan.
- Jossed. Old Time Gallifrey remains fanon and the Eye of Harmony is never mentioned.
Thirteen is going to be traveling back to the Old Time of Gallifrey through the Boundary, but she is actually a third figure (as the Virgin New Adventures put it, there was Rassilon, Omega, and the Other). The human survivors (the "Timeless Children") are actually the first colonists of Gallifrey, and the Doctor will help to turn them into the Time Lords. That's the horrible secret that drove the Master into a fit of murder; the Doctor and humanity are the source of the Time Lords.
This also explains Ruth. The Doctor founds Gallifrey along with the other Time Lord legends, then erases her own memory of the entire event (which we saw her do to others in "Spyfall") for unknown reasons. Ruth actually is a future Doctor. The Doctor stops the Master in the past, preventing Gallifrey's destruction, but ends up never remembering it was ever destroyed. She's remembering Gallifrey after it was restored this season, not the Gallifrey from "Hell Bent."
- Mostly Jossed. The Doctor is arguably one of the founders of the Time Lords, and her memory was erased. But everything else is false.
In "Orphan 55," the Doctor states that the wrecked, abandoned Earth is only "one possible future." Gallifrey is caught between two possible pasts. Whittaker Thirteen and the Dhawan Master come from one; Martin's Doctor (Ruth) comes from the other. They're not alternate universes; it's more like Schroedinger's cat, where there are possibilities but nothing yet decided. Thirteen will end up with a choice: either stop the Cybermen, save humanity, and allow Gallifrey to remain destroyed, OR save Gallifrey, doom humanity to lose the Cyber-Wars in the far future, and become a "Timeless Child" (because by so doing, she wipes out her own past, and Jo Martin becomes the current Doctor, and Whittaker's character becomes lost in a timeline she no longer has an origin in).
This makes the Judoon look even stupider than usual. Even when they find the right person, it's still the wrong person! This is how the Time Lords can dispatch bounty hunters to find the Doctor even though Whittaker has recently confirmed Gallifrey is just a smoking ruin.
- Jossed, completely.
Throughout the Episode, we see the life of some one called Brendan, who seems some what disconnected with the rest of the Story. In his life, we see he joins the Police, gets shot and falls off a cliff but recovers almost instantly, before seemingly getting his mind wiped. What if what happens to Brendan is actually supposed to be shown as a metaphor for the Doctor?
Granted, this theory depends on the assumption that Ruth's Doctor is between Troughton & Pertwee's Doctor. What if it begins with the Second Doctor working for the Time Lords, as seen in The Two Doctors as well as the Season Six-B Theory, but during this time he got shot and fell, causing him to Regenerate in to Ruth's Doctor. After some time with Ruth's Doctor, the Time Lords then wiped her memory and exiled her to Earth as the Third Doctor.
It does show the Time Lords can change the Doctor's Memories, having taken their Knowledge of how to work the TARDIS, so it could also mean they either took or changed the memory of Ruth's Doctor, too?
- Partially Confirmed: While not between the Second & Third Doctor, Brendan IS supposed to be the Doctor. All the scenes are glimpses into the Doctor's history, encoded as the history of an unknown human.
- Jossed. The Cybermen had Gallifrey on their kill list, but the Master contacts them through the Boundary in a scheme to obtain the Cyberium and some cyberconversion units and, once again, create his own army of Cybermen.
- Jossed. Fans mistook the uncredited actor who played old Brendan for McElhinney and there is no connection between the two characters.
- The very first Doctor: Especially if Ruth turns out to have been an earlier Doctor, it's clear that prior to the First Doctor all of the Doctors' lives — and Time Lords' lives in general — have involved a mindwipe at least once. Ruth may have been the first one to try and escape this fate, but the First Doctor was the first one who succeeded. Brendan is the very first because no other Doctor can start as an infant. But from the beginning they have wanted to help others and make a difference in the universe.
- Partially confirmed: He's not the Doctor's very first life, but he is a past life of the Doctor, with the memories encoded to look like "Ireland" so they would seem innocuous.
- Ashad: Perhaps the defective nature that required him to keep getting mindwiped was why he wasn't seen as an ideal "traditional" Cyberman. Also, both volunteered for their causes.
- The Timeless Child: The suffering of Brendan over multiple lives or even within the original one depicted in this episode allowed the traditional Time Lords to be engineered, as in the alternative theory above that the characters in question are Rassilon, Omega and the Other. This identity is also the only one in which the character can have the indestructible qualities Brendan has.
- All three: Timey-wimey stuff involving Gallifrey in "The Timeless Children" mean Ashad becomes the Timeless Child who becomes the Doctor, or the Timeless Child becomes Ashad who becomes the Doctor (or at least Time Lord progentior being). That the Time Lords "evolved" from Cybermen would certainly be a dark enough secret for the Master to give up on Gallifrey and destroy it.
- The Master: These scenes are repressed memories of the Master's Timeless Child and the Doctor's Timeless Child is the little girl we've seen before.
- Captain Jack: He is being held prisoner in some kind of Virtual Reality, being experimented on by whoever he was running from in Fugitive of the Judoon.
- If they enter the Boundary at a early point in history, and later they could do the Timeless Child experiments as part of creating the Time Lord blueprint.
- This will include at least one of the Doctor's companions, who for some reason will have/decide to stay there.
- Jossed.
- All the people except Brendan are programs.
- Partially confirmed: It's revealed that the Brendan situation is actually memories of one of the Doctor's forgotten past lives, placed under an encoded disguise to make them seem innocuous.
- In this fantasy world, Brendan's service is a way to seduce new converts, and the electric shock represents full conversion when their old emotions, memories and identity are taken away. "We have to get rid of everything, I'm afraid."
- Jossed.
