No solid information from me, but I'd wager that there is some assumptions built into their model related to Giga Tx. Frankly, their model is probably relatively complex. Global demand historical vs forecasted, with each factories production trends and estimations going forward. That being said, they haven't opened a lot of the new giga factories yet. So there is a lot of "error" possible in any future trending, especially when you're looking at things like "We have no idea how long regulators will take to approve the factory". Once the factory is in operation, it takes time (months) just to see where the production is versus your previous estimations, and adjust accordingly.
Anyone on order, myself included, can hope that Texas isn't baked into the current EDD's - but it probably is to some level. My date has already "slipped" from August to September.