For the validity of an IOU, the following factors need to be considered:
Timeliness: The laws of each country or region have provisions on the timeliness of debts. The statute of limitations refers to the period within which creditors can exercise their right to recover debts. Once this statutory period has passed, the creditor will not be able to recover the debt through legal means. The length of this limitation period varies depending on the country's laws and can range from a few years to decades.
The legal provisions at the time of the conclusion of the contract: If the IOU is signed within the limitation period prescribed by law, the IOU is still valid. However, it is important to note that even if the IOU is still valid, the creditor may face evidentiary difficulties in recovering the amount owed, as the relevant evidence may not be readily available or people's memories may become blurred over time.
Recognition or partial repayment of debt: If the debtor acknowledges the debt or makes a partial repayment within the limitation period, the limitation period may be reactivated so that the debt remains valid.
It is important to emphasize that the information I have provided is only a general overview and the specific situation may vary depending on the legal provisions of the country and region. If you want to know the specifics of a debt, please consult a local lawyer or legal professional who will provide you with accurate legal advice based on the laws of your location. Only a professional can assess your specific situation and provide specific legal guidance.