I concur with everyone else here. I own 4 Marshall cabs. All 4 were used when I bought them, and all four had not only loose baffle screws, but loose speaker screws as well. I tightened everything down in all of them, and they all sounded noticeably different afterwards.
I also always put a piece of foam on the back of the middle brace, and a screw through the back of the cab into the brace. I like my cabs super tight with fast response, so this may not be for everyone.