Library Transferred But iTunes Can't Find 1/2 of the Tracks! Help!

Question

Okay, I am repeatedly having this problem and I'm tired of spending a whole day (hours & hours) every time it happens. I like to run my iTunes off an external hard drive because the library is so large it would clog up two of my three computers anyway. Only my home desktop has the capacity to hold my music library and I keep a full back-up copy of it loaded on there anyway. My laptop's tiny hard drive wouldn't even be large enough to load my monster library. And I couldn't load it on my office machine if I wanted to. sigh
Anyway, when I have had to transfer my back-up library (I've had two computer crashes which required it sigh) and when I have had to replace my laptop and set it up again... and basically each and every time I set up a computer to recognize the library on the external hard drive, this has happened...
Okay, I do all the full protocol. If restoring a back-up, then obviously I copy over all the iTunes Media folder contents. If just getting the machine to recognize the external hard drive, then I copy the Music library files and I set up the preferences to point to the external drive. No problem. iTunes finds the drive, all my music files etc. pop up with all my playlists. You'd think we'd be in business.
But if you try to play them or sync, a curious thing happens. It will be able to find like 1/2 or 2/3 or whatever of them... but like a gazillion songs and movies it won't be able to find. They're right out there... and they're listed... but it claims it can't find them. If I go to play it... it will ask if I want to go manually locate it. So, I do... then it will say, if I want it to try and find the other missing content based on its location. Sure I do. It tries and sometimes finds some of it. But, invariably, I end up sitting there, every stinking time, and manually finding like 100 or 200 songs or movies. Can you spell T-E-D-I-0-U-S????
Can anyone suggest why it is doing this and how to fix it? Oh yeah... and of course my library is consolidated and I let it manage/organize it... though it really seems to be jumbling and mixing thing up ever since I did ... cuz I notice now that not all my audiobooks are together... I've got stuff in weird grouped files... so I think it is drunk... but if I were to rearrange it... Lord Knows it would probably never find anything again. Grrrrr.

Answer 1

The biggest problem with an exHD is when windows decides to give it a different drive letter without asking/telling you. This can make itunes lose the paths to songs. It's easy to fix but a lot of people don't know to do it: assign a permanent drive letter to the exHD.
http://support.apple.com/kb/TS1493#changedrive
Another thing, when you do this
+Okay, I do all the full protocol. If restoring a back-up, then obviously I copy over all the iTunes Media folder contents+
You are only getting part of itunes. There is itunes library content and the itunes library database. The content is all the songs, movies, podcasts, etc.
The database is the play lists, ratings, play counts, etc.
The default for the database is always on the C: drive unless you move it to the exHD and do a shift-start. That is the way mine is set up.