Changing iMovie Original Media File Location

Hi, I am trying to organize almost 20 years worth of videos in iMovie and I'm struggling with the file structure. My overriding issues is that every time I get a new computer (about every 8-10 years), moving iMovie libraries to the new computer invariably breaks my links from the library to the original media files. So I'm (once again) going through the process of reimporting the original media to iMovie, but I'd like to have some organization system that I can understand such that when I eventually get a new Mac down the line, I won't have to do this all over again.

To make my libraries more manageable, I have separated them by year range. So I have a 2006-2009 library, and 2010-2013 library, a 2014-2017 library... etc. All of these are located on an external SSD (formatted APFS) called "T7 Shield" in a folder named "iMovie"

The issue is some of the libraries (the last 3) point to original media within the "Final Cut original media" folder on the "T7 Shield" drive in the same "iMovie" folder as my iMovie libraries. I also have a second external drive named "T7". It is also an SSD formatted as APFS. The first two libraries (2006-2009 and 2010-2013) point to the original media files in an "iMovie" folder on the "T7" drive. I'd like to have everything consolidated together in the same folder so I don't have to piece together where everything is the next time I have to move my iMovie libraries to a new computer. I have no idea why the first two libraries point to the original media files on a completely different drive from the last 3 libraries. And I can't find anywhere within iMovie to change where original media files are stored. the other thing I've noticed is the first two movie files are SIGNIFICANTLY larger than the last 3. It's almost as if the media is stored within the library (and when I moved my libraries to a new computer the links did NOT break for these first two libraries).

So I guess my questions are:

1) how do I tell iMovie where to store the original media files and get everything consolidated under a single "Final Cut Original Media" folder

2) How do I move these to another computer without re-breaking all of the links. It is a MAJOR process to reimport everything (not to mention all of my projects get totally FUBAR'd too)

Thanks in advance for any help.