credit confuses me

So on my credit report its show two collection accounts back from when i was young and dumb. Im going to pay theese off. I have other old bills that are with a collection agency but dont show on my credit? I want to settle theese. since the balance doesnt show on my credit it shoulnt matter. one even has my year of birth wrong but everything else is right. One was showing as a collection account but was then removed? will this unpaid balance pop back up on my credit or since they removed it can they legally put it back on?