Not sure this qualifies as very long hair?
Well, it's probably close enough to qualify.

Base +10, Dasu -7, buttfarty -6, demoniosen -6

Hard to tell with a dress like this, I'd say borderline.

Working with this tag I've learned the position of the belly button is less consistent than you'd expect it to be, much more random than other body parts we've designated for these kinds of measurements.

Base +20

An easier measurement would probably be if the hair reaches the hips/butt

Base +10

It would be, but that's would also require it to be about a hand's width longer (on average) than the current requirement, belly button was probably chosen to make it a little bit more accessible.

Base +20

True, going back and reevaluating all the existing tags would not be fun

Base +10