With a New York City co-op the proof of your ownership is your stock certificate and proprietary lease. In a co-op, you don’t own the apartment but rather you own shares in a corporation. Getting a new stock certificate can be an onerous process depending on the building and management. If you have a loan, your lender probably has it as collateral so check with them first. If not then it can be more expensive to recover. Read the full article here.