IPhoto is not recognizing all the photos on an external drive

Question

I used Migration Assistant to transfer accounts and data (with the exception of photos and music from one user) from a 320 gb hard drive (from a broken PPC iMac running Tiger 10.4.11) to a 160 gb Intel iMac running Snow Leopard 10.6.8. When I opened iPhoto 6.0.6, it prompted me to locate an iPhoto library, so I pointed to the iPhoto Library folder on the old hard drive (Users/Name/Pictures/iPhoto Library).
Everything seems fine except that about half the newest images from 2011 and all the images from 2012 are missing. The folders appear on the left side, but they are simply missing the rolls and images. The images do appear, however, in the Originals and Data folders on the old hard drive in the corresponding 2011 and 2012 folders. I can view the images if I double click them.
I tried manually dragging one of the "missing" rolls from the Originals folder on the old hard drive to the iPhoto application, but it did not work. I got the green "+" sign, and it attempted to import the folder as usual, but then a message popped up that read, "Unreadable Files: 1 The following file could not be imported. (The file is in the iPhoto Library folder.)."
Please advise.
Thank you in advance.
-Don

Answer 1

I'm no sure I understand this:
I used Migration Assistant to transfer accounts and data (with the exception of photos and music from one user) from a 320 gb hard drive (from a broken PPC iMac running Tiger 10.4.11) to a 160 gb Intel iMac running Snow Leopard 10.6.8.
So you moved the accounts and data from the old machine to a newer one.
So, why then did you point iPhoto at the old machine?
so I pointed to the iPhoto Library folder on the old hard drive (Users/Name/Pictures/iPhoto Library).
Or do I misunderstand you?
This is a symptom of a corrupted Library:
The folders appear on the left side, but they are simply missing the rolls and images. The images do appear, however, in the Originals and Data folders on the old hard drive in the corresponding 2011 and 2012 folders. I can view the images if I double click them.
Assuming you a: copied the Library to a new location and b: it worked fine in the previous lication, then I would guess the copy went wrong. Re-do it, manually, don't use Migration Assisstant.
If you didn't move the Library then
Try these in order - from best option on down...
1. Do you have an up-to-date back up? If so, try copy the library6.iphoto file from the back up to the iPhoto Library allowing it to overwrite the damaged file.
2. Download iPhoto Library Manager and use its rebuild function. (In Library Manager it's the FIle -> Rebuild command)
This will create an entirely new library. It will then copy (or try to) your photos and all the associated metadata and versions to this new Library, and arrange it as close as it can to what you had in the damaged Library. It does this based on information it finds in the iPhoto sharing mechanism - but that means that things not shared won't be there, so no slideshows, books or calendars, for instance - but it should get all your events, albums and keywords, faces and places back.
Because this process creates an entirely new library and leaves your old one untouched, it is non-destructive, and if you're not happy with the results you can simply return to your old one. 
3. If neither of these work then you'll need to create and populate a new library.
To create and populate a new *iPhoto 6* library:
Note this will give you a working library with the same Rolls and pictures as before, however, you will lose your albums, keywords, modified versions, books, calendars etc.
Move the iPhoto Library to the desktop
Launch iPhoto. It will ask if you wish to create a new Library. Say Yes.
Go into the iPhoto Library on your desktop and find the Originals folder. From the Originals folder drag the individual Roll Folders to the iPhoto Window and it will recreate them in the new library.
When you're sure all is well you can delete the iPhoto Library on your desktop.
In the future, in addition to your usual back up routine, you might like to make a copy of the library6.iPhoto file whenever you have made changes to the library as protection against database corruption.