[Koha] Reports issues

When I do a report on 'issues by category' I get a total of 1466 items. A note here; I only get results if I don't check the branch - we have only one branch, main, and if I do check that, I get only zero's. So, if I don't check that I get a total of 1466 items issued. We have a total of 6627 items. When I do a report on 'books not issued' it comes up with a total of 5700. Maybe I am all wrong, but in my world, 6627 - 5700 = 927, not 1466. (Total minus items not issued is number of items issued) So, is my thinking wrong or is there something wrong with the report? And what can I do about it? Is there any way to test it? Thanks, Marty