While I do not qualify for the Netherlands part, I personally would argue that three archeological sources Ancient Babylonian Chronicle 19 Weidner Chronicle (ABC19), Sumerian King List (SKL) and Ur III Sumerian King List (USKL) all contain tropes, characters and narratives seemingly downstream of the OL Frisian language ones e.g. Finnish or "Gutian" sadness, Inka and Finns/Suomi as "Inki-cuc" as detailed at length in the Authenticity Debate sub-forum. Of these the SKL example in Weld-Blundell Prism is dated by academics at ~1800 BC.Putting a call out to anyone from the Netherlands to post links of the oldest examples of Frisian language being inscribed on artifacts in the real world, whether in texts or, even better, on artifacts.
The same parallels are also evidence that specifically the Norse saga language versions also must have existed at same era e.g. repeated earls (jarls) as repeated "yarlas", sons of Fornjót under their specifically Norse language alternative names (Ægir, Kári, Logi) and so on. Even this may not be what mr. Saccoccio is looking for, as we do not have the European primary materials of that same era, but instead the Levantine clay tablet echoes of those same war stories embedded among and inbetween the local Levantine materials.
If anyone reading this happens to hang around in the same spheres as mr. Saccoccio does, please forward to him a link to this forum for his further study of the OL topic.