CRM Interaction History Filtering

Hello,

Our users are confused due to the fact that at times the list of opportunities listed for an account in an Account's Interaction History doesn't match an Opportunity Query for the same Account.

I am trying to determine what filters are applied by CRM when looking at Interaction History for and Account. I have heard that Closed Opportunities are excluded, don't know if this is true for sure. Anyone have an idea on these filters?

Thanks,

Dane