Is there any protocols to identify what sort of document MS-408 is?

[magnesium]

Another good point. Entropy (contrary to age) is just a number. There is a whole frequency distribution of fractions adding up to one behind it. There are infinitely many very different distrubutions with the same entropy.

This is true, and the VMS's low entropy also places fundamental information-theoretic constraints. If you are trying to reconcile Voynichese with meaningful European text via some kind of letter- or phoneme-based cipher, you can have a lot of plaintext rearranging (e.g., alphabetization), high verbosity within the cipher alphabet(s), or some intermediate mix of both. Abbreviations could shape things on the margins, but they alone cannot be driving the low entropy.