This seems to work pretty well, if you notice that some of your thumbnails in a projct are incorrect (do not match the picture):
First, close Aperture.
Go into Finder and find your Aperture library (look in Aperture preferences to see where it lives).
Now right-click on that library and select "Show Package Contents".
This will open up a new finder window, with a file for every project. Go to the project file that you have your wedding photos in, right click and select "Show Package Contents" again.
Now you'll get yet another finder window - in here you'll see a directory (where all your pictures in this project live BTW), and a few other files. One of them is named "AP.Thumbnails".
Take that AP.Thumbnails file, and move it to your desktop. (to keep in case of issues).
Now open up Aperture again (you can leave the Finder windows open). Go into the project with the wedding photos, and select the project management view. At first all of your thumbnails will be blank. But after a little while you'll notice that it is re-creating all of them (you do not need to visit each one to have this happen). This may take some time... but when done, hopefully they will all be correct and you will see a new AP.Thumbnails file in that same project directory. I would avoid doing anything else in Aperture until the thumbnail rebuild is complete - scroll around the project management view to see progress.
If everything is to your satisfaction, you can just throw away that AP.Thumbnails file on your desktop. If something happens (and I really can't think of what would go wrong) just close Aperture and move the file back.