Get parameters issue for yandex? From converted forum?

[Black Tiger]

I don't understand their solution on how to do this, I'm not native English.
But I got a mail about a "critical error" concerning GET parameters.

Some pages with GET parameters in the URL on your site https://www.myforums.com duplicate the contents of other pages (without GET parameters).

As an example they showed this:

• tab:
  
  https://www.myforums.com/forums/topic/2726-topic-title/?
  https://www.myforums.com/forums/topic/2726-topic-title/?tab=comments

Also they gave these examples:

• topic:
  
  https://www.myforums.com/forum/index.php?
  https://www.myforums.com/forum/index.php?topic=42193.0

which are clearly 2 different things, because first link points to the main page and second to a topic. This topic in fact does not even exists anymore.

I never had a mail from Yandex before, but on investigating this, these are url's from my old IPB forum which was converted to Xenforo via the convertor almost a year ago.

I use these rewrite rules from the beginning:

        # IPS Rewrite Rules
        RewriteCond %{REQUEST_URI} /(topic|forum|user)/ [OR]
        RewriteCond %{QUERY_STRING} (^|&)show(topic|forum|user)= [OR]
        RewriteCond %{QUERY_STRING} ^/(topic|forum|user)/ [OR]
        RewriteCond %{PATH_INFO} ^/(topic|forum|user)/
        RewriteRule ^.*$ ips2xf.php [NC,L]

        RewriteCond %{REQUEST_FILENAME} -f [OR]
        RewriteCond %{REQUEST_FILENAME} -l [OR]
        RewriteCond %{REQUEST_FILENAME} -d
        RewriteRule ^.*$ - [NC,L]
        RewriteRule ^(data/|js/|styles/|install/|favicon\.ico|crossdomain\.xml|robots\.txt) - [NC,L]
        RewriteRule ^.*$ index.php [NC,L]

So how is Yandex able to find these old threads with the old url's? Because they should not be present in sitemaps anymore, and they are not present in my forum anymore either.

Can I do anything to fix this or should I ignore this?