Nice tool! I also wrote some library processing code over ten years ago, so here's some tips:
The library version only ever gets increased if there is a change in the binary format. Your tool just blindly takes any XMPlay library and assumes that it has the expected format. So you should reject any library version except for the ones that you explicitly support. Ignoring the library version is not forwards-compatible, because the tool will just read garbage once a library version 7 file is tried to be processed.
The lowest library version I have any information on is version 3, which includes all the information up to and including the song flags (except for "subsongs", see below).
Version 4 adds the rating, and version 5 adds the subsong count and subsong number.
I think the subsong field (after the file type) is the only addition in version 6, as that is missing in my old tool that only support version 3 to 5.
So, either your tool should reject and version number other than 6, or you could add support for versions 3 through 5 by reading the fields that I mentioned above conditionally. Hope that helps!