I pulled a complete list of all leads in our database. I then pulled 5 separate reports using only a single filter - one for each region we segment by and one with region IS EMPTY. Adding these up I get a different number than the DB number I get when I click on All Leads. Same happens for marketable leads - I get a different number when I add together all 5 than the marketable lead # given by Marketo. What gives?
First, perhaps try the refresh button located at the bottom of the screen before you hit export.
Also, how far are you out? A few or a few hundred or a few thousand?
Yes, that will make a huge diff. The database is always shifting here.
Also, it sounds like your filters may be causing you issues, even though you tried to use Region IS EMPTY.
When you say "regions you segment by", do you mean you have set up a Marketo Segmentation using these criteria, or just that you are segmenting your leads as a typical internal business rule?
If the former, I suspect you could take a quick peek at the Segmentation tab for a bit more info.