So I have two laptops. One I used to run Serato on with an external HD with, it has the iTunes xml and everything iTunes on it, and about 15000 tracks/samples. I have a newer laptop which I run without an external HD. It has about 25000 tracks on it. Today I was on the newer laptop and opened iTunes with the external HD of the other laptop plugged into it. It then automatically, and super quickly added all the songs from the external HD to my newer computers iTunes library. I unplugged the external HD but all these songs are still there. When I open iTunes now, it's always determining gapless playback for about 14000 songs.

All the new tracks that have been added automatically have been put in with existing dates of when they were previously added so the sort by date function does nothing to solve this. I don't want any of these song clogging up my library, what can I do?

Within the iTunes Advanced Preferences tab, do you have the option "copy files to the iTunes Music folder when adding to library" checked?

If so, those tracks added to iTunes have been copied to your internal iTunes Music folder and are there to stay :(