What is the statute of limitations on a royalty contract?

There are often provisions in Licensing (Royalty) contracts that discuss audit rights. If no clause exists in the agreement then it is 3 years (in California) for breach of written contract. Not sure about NJ. If Fraud is involved there is a much longer statute of lims.

If the contract is still in effect, then it may have a provision regarding auditing. Sometime that provision is limited by time. For example, allowing an audit of no more than the last two years. If the contract does not permit auditing, you might be able to force the issue by working with an attorney.

You should go to a lawyer right away with the contract. Most likely, the contract stated a "Choice of Law." That is a clause that names the law of which state you are going to use for the contract. The court will apply the substantive law of the state that was chosen in the contract, and the procedural law of the forum state. Statute of limits is usually considered procedural. If you go into court in a different state than the state named in the contract, however, the court will usually apply the statute of limitations that is the shorter of the two, unless you are a resident of the forum in which you seek jurisdiction. So, the upshot is that I cannot answer this question for you and you need to bring your contract to a lawyer very quickly, preferably today.