What is the difference between archival and archivable? Archival appears to be an acceptable word among official sources, whereas archivable/archiveable does not appear to be a valid entry. Is the correct form of the word describing something's ability to be archived archival or archivable? Are the two redundant, or are the official online lexicon sources just not up to date or comprehensive enough?
Archivable means "capable of being archived", while archival means "pertaining to an archive". Not the same thing at all. Both archivable and archival have a Wiktionary entry. Archivable is not too common a word, though, as demonstrated by its having only one hit in COCA, as opposed to 1202 hits for archival. That should explain why it's not in every dictionary, as not every dictionary has every uncommon word.
archival appears to mean "to do with archiving" or "of archive quality or standard".
Something that you can archive is therefore not "archival". Then again, I doubt there is any need for an adjective that indicates something can be archived. If I have a pile of documents, each and every document can be archived, whether I do it or not.
I doubt there will often be an actual conversation or discussion about the "archivableness" of objects, like
Well, I can't see how trees or people can be archived.
Sure, they can't. But files and documents are archivable.
If you want to indicate that something should be archived, archivable would not make sense, as it just indicates an object's ability to be archived.
You could just mark or name it "to be archived".