Yup...that is why the California rating system came out cause they felt the mfr. test conditions were way too optimistic even though the mfr. system is still what is advertised. Under the California "real world" testing the actual performance of ANY panel is almost always significantly less than the mfr. gives. Dog posted the site before but if you want to see how almost any panel performs before you buy...check here...
Eligible Photovoltaic Modules