and you should see an exclamation mark next to the ones that it has lost track of.
Failing that, try to play the ones that you say it skips and, if it cannot find the track, it should ask you to locate it.
I don't know of a "Rebuild" function in iTunes
I have over 750 songs. While fooling around with iTunes I found an area that had what I, as a tech idiot, thought were duplicates taking up space. I started going through the list and deleting songs. Now when I use Shuffle Songs it misses many of those songs I deleted, even though they are still in my iTunes and I can play them by selecting them. I need to rebuild or repopulate that area that I deleted from. How do I do that? Thanks.