As of this moment, none of the fics in The Truthseekerverse have an AU tag. And I'm hoping to keep it that way for as long as possible.

That said, I do not want the authors to "play it safe". I LOVE worldbuilding. And this verse should feel epic in scope. The readers should feel that this world is BIG and COMPLICATED. Use what I call "The Offscreen Battle in Tartarus Principle", For every epic event we see on the show, there is AT LEAST one other we don't. Naturally, this is almost certain to result in us needing AU tags before long, but I'm happy to pay that price.

In fact, by Word of Nayuki, ponies don't have family names, so by that standard, we are already AU. Similarly, A Debt to the Stars will completely contradict Word of Faust on the history of the Elements. As such, for the purposes of this verse, treat the words of those who have worked on the show with respect and use them as you can, but do not feel constrained by them.

As for the show, thus far, every episode up to the end of Season 3 and including Equestria Girls is considered to either have happened, or will happen. We will try to keep to this principle for future episodes if we can, but that will remain to be seen.

Similarly, the Expanded Universe material is used as much as we can. For example, I can say that as said in The Crystal Heart, Cadance used to be a pegasus before she became the alicorn of love and holder of the seat of Venus.

EDIT:

UPDATE:

With A Debt to the Stars and the start of Season Four released, we are now fully AU. The story of Equestria is at least slightly different form that of the show, but Seasons one-to-three plus Equestria Girls still happened. Outside of that, we can now do pretty much whatever we want though without contradicting each other. I think that although the start of Season four could not have hapened as shown, similar events work quite well.

Cadance used to be a pegasus before she became the alicorn of love

...sort of like how Twilight used to be a unicorn?

The space between the things we know - the so called 'knoweledge gap' is great fun to skate.

1170305 Eeyup. Of course, we haven't reached that point in the timeline yet.

Just letting you know how recent events have changed things.