I'm no expert, but did your lawyers clarify if a statute of limitation start from the date you learned there might be a discrepancy, instead of all those years ago?

While no one's hands might be clean in this, at the end of the day the party with the resources and expertise is equipped differently.

It might not hurt to get some more opinions even if they end up in the same place.

They learned about it when they signed the contract. Saying “I forgot about it“ doesn’t reset the statute of limitations.