Determining why some articles are marked for downloading and related issues

[Live System User]

Hi,

        I noticed that while in a newsgroup "*Summary..." buffer
        when I type SPC, I get the message:

              Message marked for downloading

        Going to the next message (response to same subject) and typing
        SPC `(gnus-summary-next-page)' displayed the article.

        For example, currently the gmane.emacs.devel newsgroup
        *Summary...* buffer has, from the top:

4.5k│%. │Live System User       ║ ┏●  Does anybody know how to debug a live 
Emacs process?
4.3k│R. │Eli Zaretskii          ║ ┗━━❯  
    │   │                       ║ ┏○  Re: xref rocks!
6.4k│%. │Dmitry Gutov           ║ ┣━━❯  Re: xref rocks!
5.4k│R. │Nicolas Petton         ║ ┃┣━━❯  
7.1k│ . │Robert Weiner          ║ ┃┗━━❯  


      The first article "Does anybody..." (from Thu, 28 Apr 2016)
      is marked for download.

      The second article from Eli is displayed.

      The third and forth articles displayed " marked for download".

      Why doesn't the first, third, and forth, etc articles get
      displayed?  Did Gmane expire them?

      When a message is marked for download what does that mean to
      the user?  Is there a subsequent action or command that the
      user should take to see those messages later on?  Is there an
      indication of what are those messages?  I see the "%" in the
      first and third message but the forth message has an "R"
      even though it too was marked for download.  If I exit and
      restart Gnus, will the "%" mark still be there?  Is there any
      way to display just messages with the "%" marker?  Can those
      be put in a virtual group wholesale. i.e. not one at a time,
      for perusing later on when available?  How long does the
      "mark for download" indication stay associated with a message?
      Does it go away/unmarked automatically if the message is
      permanently unavailble/expired from the server?  Or is that a
      manual action from the user?  Is there any way to know *why* a
      message was marked for download or is that a "catchall" for all
      "I can't get the article even though I have the subject of the
      article" problems with retrieving articles?

      How does a user go about managing "marked for download" articles?
      
      Does anybody know what happen to all the new articles for
      gmane.emacs.devel?  The newest one I see on Gmane for
      gmane.emacs.devel is from Thu, 28 Apr 2016.

      If I look at:

        http://lists.gnu.org/archive/html/emacs-devel/2016-06/index.html

      I see postings/aticles from June 2016 which don't appear to be
      listed on gmane.emacs.devel.

      Is anyone else experiencing a problem with using Gmane to view
      postings sent to emacs-devel that should subsequently land on
      gmane.emacs.devel?

      Thanks.