I was having a strange problem where iMovie 08 was labeling portions of the video that I imported as events occurring during 2015 and 2021. It made my Event Library really messy and I still don't know why it will decide certain pieces of the tape are from literally decades away. Segments before and after these are labeled correctly as 2007 and I have double-verified my camera's date and time settings.
I thought that I would just have to deal with it but then as a last ditch effort I decided to go take a look at the file names. When I looked in my Movies folder under 'iMovie Events' I was able to find each individual file and they were named things like 'clip-2021-05-28 16;28;08.dv.' I tried changing the name to 'clip-2007...' and lo and behold it worked! I had to quit iMovie but when I restarted the app, all my movie events were correctly placed under 2007. I imagine if you do this renaming with your older movies, it should have the same effect. Seems a bit more efficient than the Terminal code and I bet you could even tell Automator to do it for you...