If you can not get the answers you are looking for, try to find a go RE lawyer.
However unless it has cause "damage" to you, it is possible that it might not be worth your time to pursue.
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You ask about options. Well, in what way, if any, were you injured? Or what would you like to happen? I'm not a lawyer, but... If there had been more of a discrepancy than, likely, a matter of a couple of months back 18 years ago, it might be more significant. Or if, let's say, the builders in 1990 were top-grade professionals but the different builders in 1989 were low-life incompetents, and that were reflected in the prices others paid, that might be significant. And you might want to contact a lawyer.
Or if you feel that you were deliberately misled--that the agent knew the house was built in 1989 but for some reason lied to you and told you 1990--then you might contact the agent's broker.
However, my non-legal advice--barring one of those scenarios above--is to do nothing. A discrepancy, if there is one, of a couple of months on an 18 year old house is not significant.
Hope that helps.
Usually the seller's disclosure has to specify the year built on it and it asks the seller what is the source of that year, if it's the original owner, they remembered that they closed on the house in 1990 and that's what they used....
Occasionally, I do see this happen several times a year. Sellers typically rely on tax records for this type of information, but that's not always correct. Yes, the title company should reveal the truths about a property but again, they can be wrong too (rarely, but I've seen it happen).
Look at it this way: if a contractor began building the house in November 1989, but received the certification of occupancy in February 1990, then when would you say the house was built? The owner probably said it was built in 1990, and tax records may have agreed. So the seller may not have been intentionally steering you wrong. But then you go to close and perhaps the title company and/or lender says otherwise.
How did you discover it was built in '89? Did you have a Realtor or attorney representing you? If you had an agent or attorney, contact them and/or your title company as they should be able to put this to rest. But like James previously said, unless this caused you financial damage, there's no real sense in pursuing in court.
Frank Biganski, Realtor ABR