Property tax deduction on coops

The IRS doesn't, but woe to the person who has been doing it substantially incorrectly (either through ignorance or intent) and gets audited, and cannot provide a reasonable basis for their numbers (i.e., the letter from the managing agent).

In my building, the letter comes from the co-op's accounting firm, and gives the per-share amounts. The shareholder (or their accountant) is left to multiply by the number of shares they hold.

I suspect that incorrect tax deductions are only caught during audit. There may not be any systematic way for IRS to track it.

I would assume that the the IRS has some sort of algorithmic way of checking tax returns en masse to make sure the stated deductions are reasonable. If someone's deduction is some degree outside of the standard distribution, that's likely what triggers an audit.

The Coop SHOULD be sending both the shareholders and the IRS 1099's for their portion of the RET and mortgage interest every year.

Doesnt alternative minimum tax makes most of it a mute point anyway

Not if you make more than 800k-1mm.