While neither of these were registered by the companies who "own" the formats,
it is interesting to note that in the MAWG OID registry work in the EMA
Microsoft asserts that versioning and platform information is not necessary in
such fields since it is carried in the format itself, whereas Wordperfect (now
Novell) asserts that this information should be present. In other words, these
values are in fact technically aligned with how the companies have stated that
these things should be handled.
Microsoft's strategy makes negotiation of the acceptable format based
on MIME type impossible.
So, you want to have a "version=" field. Then, the other brain-dead vendor
will misuse the field and you will need yet another field, and then...
Masataka Ohta