I still have the bound, page-numbered notebook issued to me by Microsoft in the late 90s for this exact purpose, along with a lecture explaining the methodology above. (A rather misguided effort by an IP attorney who was apparently new to software…)

Still being sold:

https://www.amazon.com/BookFactory-Black-Inventors-Notebook-...

for example.

Notice some of the features: pages are sewn in, so it will be obvious if one is removed, tamper-evident archival paper, space to sign each page.

Paper documents I think still have the most standing as evidence.

This doesn't look like size for a full notary seal but space for a witness to sign. I suppose a notary could stamp it someplace.