Delegates that haven't CTEd can be contacted by telegram if you have specific questions (though they may not answer!) You can also browse their Dispatches.
You can click on the green marker at the end of a CTE'd nation's name to take you to their Boneyard entry. Any Factbooks or Dispatches they wrote should be linked from there.
The WFE Index (http://udl.taijitu.org/wfe_index/) is a great resource too. Type in the region name, and historical WFEs for the region since 6 June 2010 will be stored.
The Region Flag Archive (http://udl.taijitu.org/images/rflags/) stores flags from 11 Feb 2012
The Wayback Machine is very useful. Some region pages will have been snapped at various dates in history. Usually these snap shots were taken on days that the page was heavily visited - for example, when raiders were piling the region. You can see some of the nations that were in the region on that date, see the activity log, and some of the RMB posts too.
You can try following some of the links (eg to a nation page), and sometimes you'll get a result (although the linked page may be as at a different date from the page you just left)
Some old WFEs have forum links that may still work.
Running searches on the NS forums can be productive too. Maybe a region had an embassy thread in Gameplay. Or were proposed for a Commendation in "Security Council", or "WA Archives".
NS History - from the description, "This is a historical view of NationStates from May 2003 until today. It contains information gleaned from the the pages of "The World". We started with just The Regions, but eventually added The Nations. We have collected all the data in the three columns displayed. It will give an accurate snapshot of both regions and nation on any given day."