Moving the iPhoto library does NOT involve any importing -
Moving the iPhoto library is safe and simple - quit iPhoto and drag the iPhoto library intact as a single entity to the external drive - depress the option key and launch iPhoto using the "select library" option to point to the new location on the external drive - fully test it and then trash the old library on the internal drive (test one more time prior to emptying the trash)
And be sure that the External drive is formatted Mac OS extended (journaled) (iPhoto does not work with drives with other formats) and that it is always available prior to launching iPhoto
And backup soon and often - having your iPhoto library on an external drive is not a backup and if you are using Time Machine you need to check and be sure that TM is backing up your external drive
OK, maybe something else happened. I originally moved the iPhoto library as you said (or so I thought, I may have done something wrong...), but many of my pictures no longer showed in iPhoto. I had to re-import them, regardless of the cause.
My question is why I am having different counts, for both the number of events as well as number of photos in an event.