Yes, it is a pain.
Any author metadata that is included in a Pages '09 document will be removed when opened by Pages v5/v6, and you are informed by a warning panel. If you make no edit changes (converted to Pages v5/v6 document format), then simply quitting Pages will leave the author info intact.
If you know the Pages '09 author's name string, you can type the following in the Finder Window search box, or Spotlight to reveal all Pages documents by this author. Both of the following require Spotlight Indexing of your boot drive on the Document category.
kind:Pages author:"Jon Jones, Martian Hunter"
Also, only Pages '09 Author name(s), if present, can be revealed with the following Terminal command.
mdls -name kMDItemAuthors foo.pages
Neither of the above techniques work with any release of Pages v5/v6. You cannot get at any Pages document author name string via the Finder Get Info panel, as you can with the author attribute field of a PDF.
Pages v5/v6 only store author information for exporting to ePub, or for use in document comments. There is no programmatic means (AppleScript) to get at that author information in the document.