Generic Answer  YES

IF you cancel twice, (ie don't wait for the current files to finish), you'll
redownload those files.


BUT in some cases ACTIVE content pages can have things that change (like the
current time) if that's the case they're different than the were and will get
redownloaded, every time.

Think of a picture on a site, down load it now, and it will be the same later. 
But if that picture is the output of a web cam that updates every 20ms,  then
every time you resume/update a mirror the picture gets redownloaded\updated


and Some sites have AD content that is Active which can be a problem.