Netview 6 for NT

Is there anyway to prevent or control the historical information in
the EVENTS tab (under OBJECT PROPERTIES) from aging out?

For instance, I have a router that had some events last week,
but today the information isn't there.  I did a Demand Poll on it,
then checked EVENTS, and it now has the current date/time of that
Demand Poll.  As if, that reset it to start collecting again.
I don't know...I appreciate any ideas.

Thanks,