Once you get familar with the pillar of support, neck emergence, and LS gap, which are things that don’t change, at all, once a foal unfolds, then you can see that no matter the growth spurt, and you learn to distinguish between actual structural conformation, and postural/stance or growth “conformation”.
What you can’t tell until they’re done are back and neck length. If they’re even in a butt-high phase past around 24 months, you can’t know if they’ll finish even, but the odds go lower and lower the older they are and are still/again butt-high. When they’re butt-high that also straightens the hind end, and it can be harder to tell how that will finish up