Disappearing purchased songs from iTunes library on MacBook Air

Starting with OMG-Too many Songs I installed from BOUGHT, Paid for Music CD's way back when and now still Music I've purchased through iTunes Random out-of-the-way songs DISAPPEAR! =No wonder don't hear those songs from my iTunes anymore!! and how many I've Already RE-purchased replacing Uploaded CD-music! -I'm thinking an intentional algorithm!?? Honestly- CHA-CHING$$$

[Re-Titled by Moderator]

Original Title: Apple -iTunes keeps Stealing my already paid for music - time and Time again, update after update other Random songs SUDDENLY disapear