Regarding dulpilcate tracks...

I have just over 5000 duplicates, i'll be fuck if i know how the hell that happened

Does iTunes for example:

If theres 4 duplicate songs, will it count only 3 of them leaving 1 behind in the main music library?

I dont wanna delete all the duplicates to find out it don't do wot i fort it did do i?! lol

Any thoughts or advice?