[db-wg] improve --list-sources query to retain history

If the WG is going to look at improving the --list-sources code base, I have something that I would love to see on the wish list to be implemented..  

Maintaining history (upto the point where a prefix is leaving the RIPE DB, due to an inter-rir transfer. ) is helpful to see who the previous holder was or where the prefix came from.  

This is particular the case with Legacy prefixes that are being split up.. as it is current practise to delete the parent prefix after a prefix split and transfer.  
Once the parent is deleted, you can't list or request the history of the parent prefix anymore.  

 If the historic --list-versions and --show-version could be preserved somehow (on the original prefix size.. instead of them being deleted..), that would be very helpful.  

Regards,
Erik Bais