Length of Commission Tail

What is the typical term for a commission tail in NYC broker contracts? I (not using a buyer's broker) saw an apartment in late 2012 that was de-listed by late 2012. It was then re-listed by the same brokerage. It was then de-listed again, about 10 months ago. Shortly after it was de-listed for the second time I reached out to the selling broker to inquire if the apartment went under contract and made a soft indication of an interest to make an offer, but it seemed that the seller was not receptive at that time. I'm looking to transact directly with the seller now and trying to figure out if they will be on the hook for a commission. Thanks!