Q: Why I have each of my songs 2-3 times in iTunes

Hey Manuel,

To clear things up, it sounds like you are adding music inside of a playlist but it is from songs that are outside of iTunes. If you delete songs in your playlist and keep adding songs to a playlist from that add to library option then you will keep seeing duplicates. I would make sure that you are in your main library if you are adding songs to iTunes. To answer your second question, any changes that are made when getting info will affect the file from that point on until the next change. 

I have provided you with multiple articles for more information. If you are simply making a playlist, check out the first article to walk you through that. The second article talks about adding music into iTunes. The third article will help with removing any duplicates from iTunes. The last article will go into information about editing track information on your music. 

iTunes 12 for Mac: Create a playlist

https://support.apple.com/kb/PH19486

Add music to iTunes

https://support.apple.com/en-us/HT201169

Find and remove duplicate items in your iTunes library

https://support.apple.com/en-us/HT201812

iTunes 12 for Mac: Edit song and CD information

https://support.apple.com/kb/PH19618

Take care,

-Norm G.