Another question to satisfy my curiosity: suppose you own a small business, and a supplier ships you materials, but forgets to invoice you. You use the stuff, and years (3-5) go by without a bill from the supplier. After some time, the supplier audits his books and sends you an invoice-and your records no longer exist. My question: are you obligated to pay a bill 6 or more years old? Is such a debt enforceable in court?
Depends on where you are.
In most U.S. States, Section 2-725 of the Uniform Commercial Code (link to NY statute) provides for a 4 year statute of limitations on the sale of goods.
Note that this applies only to the sale of goods, as defined by the UCC, and not services or intangibles. In addition, there are various circumstances under which the statute of limitation may be tolled, extended, reduced or otherwise modified. The law may be different in states other than New York and in foriegn jursdictions. The laws also vary in international sales of goods, which in the U.S. are covered by treaty. This is not legal advice, and for advice concerning your particular situation, please consult a lawyer in your jurisdiction.
That being said, all else being equal, after 4 years they’d have a real tough time collecting in court on a bill for the sale of goods.