eBay keeps completed listings (Sold UnSold) for 90 days after they end.
My eBay only shows 60 days.
All other eBay tools (Selling Manager, Turbo Lister) show the full 90 days. All third party tools as far as I know (Auctiva, inkFrog, and so on) show 90 days.
Free eBay Turbo Lister can save Sold and UnSold listings forever. I have original listing from 2009 in Turbo Lister. Turbo Lister works only on Windows computers. TL can be unstable at times and lose some of your listings so one must back up often.