Nachweisschwerpunkt

18:07 Sep 27, 2011 

I like Wendy's more natural-sounding alternatives, but I think you need to incorporate the idea of "evidence" somewhere ("the main evidence of their use dates from ..." or "evidence of their use peaks in ...."), since one can argue that there is a subtle but meaningful distinction between when something was actually used and the extent of evidence of use (i.e. just because we lots of evidence from century xxx doesn't automatically mean that that was actually the time of greatest use).

12:00 Sep 27, 2011 

http://www.wordsmyth.net/?level=3&ent=emphasis or
http://www.wordsmyth.net/?level=3&ent=focus

for "Nachweisschwerpunkt" I would recommend "focus or central evidence period" since it's about time/date.

For "Umlauf...." most commonly found and for "Gebrauchs......" hub of use/implementation

Hope this is of use!