Pivot decisions are messy, and one-sided. The information we have is always incomplete, subjective and debatable. Plus, it often tells us what's not working, rather than help point us in the right direction.
In GTD, there's a concept of the Trusted System, a system that allows us to input useful things as they come up, and that we trust will bring them back to us when they're relevant. For example, we never remeber to buy milk. A Trusted System lets your record that you're out of mind at the fridge, and reminds you at the store.

The same is true for pivots, while we're out collecting information and building our startup, we come across a lot of useful options that we don't record because we don't see it as relevant to our current direction. But it's worth recording for our inevitable pivot decision later.