I can see how this procedure would seem to be the correct one. The way you described it is logical. However, the result you got is exactly what I would expect from the procedure you used. I only know this because I've been deeply involved in MC for quite a few years and have done a lot of drive manipulation.
If I were you, I would start by restoring a backup from just before the changes you made. That way you are back on the original drive with only ONE copy of everything. From there you can experiment with the procedure I'm going to talk about.
The correct way to do this in MC is to use the Rename, Move, and Copy Files tool in "Update Database" mode. When you do this, it will tell MC that your files have moved, and MC will update their file location internally. That way there's no need to reimport anything. All files will be exactly the same with all the same play counts, last played dates, and most importantly all the same playlists.
An outline of how to do this:
1. Highlight some files.
2. Tools > Library Tools > Rename Move and Copy Files
3. Inside of RM&C:
* Update Database to point to new location
* move all files : Unchecked
* Directories: Unchecked
* Filename: Unchecked
* Find and Replace: CHECKED
* Find what: Path to old drive goes here
* Replace with: Path to new drive goes here
As an example, let's say you were moving from a drive named 1TBOLD to a drive named 8TBNEW.
In Find, you would type: /Volumes/1TBOLD
In Replace you would type: /Volumes/8TBNEW
This assumes that the directory path on both drives, to the music files, is exactly the same. If not, you'll need to type more in order to do a Find and Replace that represents the new file path on the new drive. As an example:
Find: /Volumes/1TBOLD/Music/
Replace: /Volumes/8TBNEW/Backups/Music/
Now, before you press OK, look at the right hand side of the screen in the Preview area. That will show you exactly what MC is going to do. Make sure the file paths look correct. Also note that this is a COMPLETE list of what MC is going to change.
You should start by doing this to ONE FILE and see if it works. If not, restore your backup and try again. Then do maybe an album or two. Make sure they work. Then, when you are confident in the method, highlight your entire library and do all of it.
I hope this helps you. Go slow. Understand what you are doing. You'll do it correctly.
Take care,
Brian.