imovie backups sync with master?

I found a suggestion to backup iMovie to disk by copying the iMovie Library folder to a backup disk. I have plenty of backup disk constantly attached to my machine so I actually made several copies of my iMovie Library in different folders. Then one day I deleted a clip I wanted and went to my backup to pick it up. It seemed to me that the clip I deleted was deleted from all my backup copies because when I opened the backups (I went to the backup disk and clicked on that iMovie Library icon) the clip was gone from there too. And this was the same for 2 or 3 backups. Is that even possible? I have worked with disk backups for 40 years and I've never seen anything like this happen. version = iMovie 10.x