There is something very odd.
Searching for the term "thruster" as an example.
If I put "thruster" into the box top right I get 20 hits all 2006-2007
If I put "thruster" into the search icon as suggested by Martin at the default 730 days I get 20 hits April 2013 on.
If I put "thruster" into the Martin box with the oldest set at 2000 days I still get 20 hits but now around 2009.
If I put "thruster" into the Martin box with the oldest set at 9730 days I get the same 20 hits that I got when using the search box page top right.
My conclusion is that I get the oldest 20 hits from whatever date I allow as the oldest post. There is no way that I can get more than 20 returns.

This did not use to be the case.