My son will be applying to school next year for a fall 2019 start. This means that he will use our 2017 tax info for determining financial aid. That's unfortunate for us because our income is rather inconsistent from year-to-year and 2017 was an uncharacteristically high year for us. I've filled out an NPC with 2017 and projected 2018 numbers, and there's about an 18K difference in our EFC. (That was for MIT, a CSS Profile school -- all the schools we'd be looking for need-based aid from will be Profile schools.) By the time we hit financial aid application deadlines, we will have 2018 taxes done as well. I'm sure this varies on a case by case basis, but will schools typically consider 2018 income information if it differs significantly from 2017? (And yes, I do put away extra money for college when we have a strong year, but we also have some deferred maintenance on our house to deal with.)
In the past, 2018 would have been the tax year to be considered for 2019-20 financial aid, and I know they changed that to make it less of a rush to get taxes done before finaid deadlines (which in general, I really do appreciate) but in cases where there is a significant difference, I hope schools will still consider the newer information as well.