How common are assessments in Manhattan co-ops?

you learned this in contract? Your lawyer reviewed the building docs but allowed you to sign and THEN told you about the assessments? Shitty lawyer. Yes -- in the last 7 years, there have been many assessments in my coops for upgrades and unexpected spikes in property costs.

Ideally the co-op or condo board anticipates everything when drawing up the next year's budget, and plans a few years ahead, too. If not, it can borrow or assess. If planning ahead, it can raise the maintenance/CCs to stash the money away.

Agree with manhattanfox that there's no reason for the assessments not to have been obvious in the financials. Even if the assessment income wasn't broken out separately from the maintenance/CC income, the discrepancy would've shown up.

No contract yet, attorney raised this after reviewing financials and board minutes

The coop I previously lived in assessed almost every year, but they were very small, often a one time payment of $100. If the building has a low reserve, expect to be assessed often. The thinking is that it is better to pay as you go then assess just to put the money in the savings account for a rainy day. I sort of think of assessments as a one time charge for when a roof needs repair or a boiler breaks in a house. Better to have savings in your own account, and expect to do it once a year.