yeah..it's tough to get all your brass back even in the local matches. I get about 50-60% if i am lucky. I mark my brass different colors so i know right away it's mine or not. However usually they try and keep the squads moving fairly quickly so you don't get much time to pick up brass.
I usually wait till the day is over and sort thru the brass on the range.
It's hard to be not so anal about brass.........