The angle I haven't heard, yet I think would make the most sense, is that you both understood the agreement correctly, at the time.
Somebody did the paperwork wrong, but paperwork isn't the agreement. You agreed what you agreed, thought everything was in order, and then discovered an error in the documents.
It doesn't seem like there's a claim here.
Depends upon the canon of construction for written contracts that you accept as correct.
At the risk of being reductive, I think that under the common law, contract terms are usually interpreted objectively unless they are ambiguous, in which case you might consider extraneous evidence. Clear language is enforced as written.