As Dan notes:
It’s the ZiPS you love/like/hate, now slightly less accurate! Predicting the future is foggy and the further you go, the thicker the fog gets. Every time ZiPS runs a projection, it provides a player’s rest-of-career projection, but until now, only the first-year projection has been made public on a systematic basis.
ZiPS is a non-parametric model, deriving aging curves from very large groups of similar players, so history is the main guide. After all, there’s no experimental data; it’d be nice to let Jose Altuve play out his career a million times in a million realities and see how he ages, but that’s currently impossible. Plus, the MLBPA probably would not be open to participating in this unending purgatory.
The three-year projections are start-of-season projections. There’s currently no mechanism to update future projections the same way the in-season projections are calculated. The year-to-year model that ZiPS uses is much more robust than the in-season model and I am not smart enough to have figured out an automatic workaround yet.
David Appelman is the creator of FanGraphs.