"special assessment - abatement" as income?

It's just bookkeeping. See http://streeteasy.com/nyc/talk/discussion/23806-coop-assessment-lump-sum-payment

As NWT says, it's just bookeeping.
It's a way of showing "less maintenance cost" to each unit.

See if everyone gets the 15% abatement directly, your overall maintenance would cost 15% more to cover the missing "income" to run the building.
By keeping the abatement through an assessment against it, it gives the "appearance" of a lower monthly maintenance.

This was somewhat easy to do as it was mostly equitable.
However now where the state (Cuomo) has become stricter on and requires it to be a primary residence, it will be trickier to find an equitable solution for all residents with this bookeeping.

Got it...that makes sense. Thanks!