Shalka?
Dimensions in Time?
16 versions of Shada?
The last eighth doctor novel went to lengths to make all the contradictions of the wilderness years (even the ones that didn’t quite happen) possible all at once. Big Finish did something similar around Zagreus as well, if memory serves. A way to sort of knit it all together ready for the then nascent new series.
The novel was The Gallifrey Chronicles, and there’s loads of stuff in interviews what have you (including the legendary ‘we can’t do the time war somewhere else because the Beeb have rules about that sort of thing’ articles and discussions)