Music missing in itunes but on hard drive

I have a 2017 MacBook Air

I have an external hard drive with over 25,000 songs

The hard drive music is a mix of

itunes purchases
CD's i have imported to the ext hard drive
Music i have copied from other peoples hard drives over the years (which they have legitimately acquired i should add)

When i import the music to my MacBook, I only get around 4500 tracks....

What would cause this to happen?

How do i get those other files into ITunes.....?

Appreciate anyone's comments or help..........really frustrating me at the moment

最後更新：2017-09-05 16:53:10