Welcome. Did you import them? You can use the Library Tool called "Move, Copy, Rename" to assign tags according to directories.
Shouldn't that be "fill properties from filename"?
and, pd77, yes, MC will handle the entire job in one batch with aplomb! The trick is to do one or two or three at first to make sure you're happy with the result, then select the whole lot, and repeat.
If the entire 15 year catalogue is filed by "[base path]\[year]\[event]\filename.ext" then you can select a few, right click on the selection, choose "Library Tools > Fill properties from filename" and enter the following in the directory field: [Year]\[Event]
If the file names are insignificant, uncheck that field to have it ignored, or perhaps leave it checked and enter [name] in there to have the name field filled with the file name. (this should already be the case though). Don't worry about needless work, MC will auto skip files that don't require a tag update.
Once that's done, and you're happy, creating a view for theater view based around the year and event tags is reasonably simple affair and doesn't require that you move the files from their current location. If you get the tags right first, then shout back and you'll get some pretty prompt help with setting the view up for the big screen.
-marko