The “lore” is based entirely on what the Doctor knows or has been shown on the series up to now. If the Doctor learned that she had a life before her first regeneration it wouldn’t upset what has been shown because the Doctor has no way of knowing that. Nothing has happened has been changed, it’s just new information given about her and her past that even she didn’t know about.I don't like the theory that Ruth/Doc is a pre-Hartnell doctor because I feel like it would undermine Doctor who lore. But it could fit with the "timeless child" arc and the Master's warning about the Time Lords lying if the Doctor had a whole set of regenerations before Hartnell and wiped the Doctor's memories against the Doctor's will.
But I prefer the theory that Ruth/Doc is a Doctor from a parallel universe. It would be interesting to explore the concept of parallel universes where a Doctor experienced a different timeline. Maybe when the Master nuked Gallifrey, he inadvertently created a parallel universe. Ruth/Doc and Gat are from a parallel universe where Gallifrey still exists.
It’s really just a problem for the makers of the those videos of all the Doctor’s regenerations, now they have to re-edit all of them.