If you can't determine the harvest location, then the product isn't compliant with the credit, so I don't see that it matters for your LEED documentation. Please correct me if I'm wrong.
Hi Robin, as Tristan stated above, if you cannot determine the harvest location for a material that you are using on a LEED project then you cannot earn the MRc5 credit. My best advice is to do your best in researching and uncovering the harvest location though some supply chain investigation. For example, if you know where a specific material is manufactured, then you may be able to contact that manufacturer for information regarding where they get their raw supplies from. Hope this helps a little and good luck.