In CMDB Query builder:

(1) run query1 which shows a total e.g. 500 results.

(2) run query2 which shows a total e.g. 10 results.

(3) run query3 which adds an OR operator to connect both queries e.g. this should combined the results but it is showing only 300 results.

New York Patch 4

In the 3rd query where you combine relationships, check if there is a reverse direction relationship e.g.between cluster resource and computer

cluster resource
<== defines resources for:: Gets resources from == computer

You can test by removing the reversal to see if you get an accurate count

I found a known issue PRB1322943 fixed in Orlando in regard to 2nd level relationships which you can apply and test to see if this also resolves relationships which are reversed.