Well it may not be the
right way to do this, but sorting it out was a lot easier than I thought.
I disabled sidecar creation and trashed the existing files (
I want rid of them anyway) along with the cover art.
I then created a new calculated Library field for missing files using
ismissing(), and grouped the files by [Missing]
Next step: Library Tools > Rename, Move, & Copy Files... >
Update database to point to new location.
I did a simple replace with
X:\Video and
D:\VideoFiles which were found are grouped together under "0" (because they are
not missing, and
ismissing() returns 0 for that) and files which are still missing are grouped under "1"
Now select all files which are still missing, and move on to the next drive letter, so replace
D:\Video with
E:\VideoRefresh the view, replace
E:\Video with
F:\Video and so on.
Only took a couple of minutes to fix the links on all drives.
Before that I did try backing up my library first, and letting auto-import have a go at it, but I just ended up with a ton of duplicate files that had a new import date, no ratings etc.