Different genres on external hard drive

Hi: I just moved my itunes library to a mybook live external hard drive following these instructions (http://support.apple.com/kb/HT1449). Everything works fairly well, except there are a few genres that appear on my music player (Tivoli AudioNetworks), streaming from my external hard drive, that *do not* appear in my itunes library. Also, a few songs have one genre on the external hard drive/Tivoli, but have the old genre when I access itunes via my laptop.

the songs are physically only located on the external hard drive and the old iTunes media folder as been deleted from the trash on my laptop.

How is genre information encoded? Can any one shed any light on this?