Through my experience I have seen very few cases when a validation is not required. I believe a lot of the requirements come from internal pressure and may not be directly required by the FDA or ISO audits. When in doubt validate. It seems that you are in a way worse situation if a validation was not executed when it was needed than to validate a product that might not have needed to be validated. The validation process can be tedious and often the individuals requiring you to validate are not the ones that need to do the process. It can be annoying to validate a product that seems very unnecessary to validate, but it is always better to be safe than sorry.