Other files than the "reserved files" in META-INF?

Context: I am finishing up support for EPUB for C2PA and the logical place to put the Content Credentials (aka C2PA Manifest Store) is in META-INF.

Reading over the 3.3 spec, it is clear in 4.2.2 that the publication itself can’t put additional files inside META-INF.  However, it is not clear (either there or in 4.2.6) if there is any restriction on a processing system can place files there that are not referenced.

So any problem with my putting our `content_credentials.c2pa` file in there?   If there is, any other recommendations – just the root?

Thanks,
Leonard