2002 Buick lesabre radio questions

I just bought a 2002 Buick Lesabre and it has a 12 disc CD changer in the trunk. They guy i bought i from took out the factory radio and installed a aftermarket unit. He said that once you remove the factory radio, the disc changer wont work anymore. I call BS because i think it has something to do with the Theftlock system in the radio, if im not mistaken. Now my question is this: if the theftlock has been activated, is there a way to reset the radio to get it to work, and if so, would that get the cd changer working again? any and all info is greatly appreciated!!

I think 2002 was the year they changed unlocking the radio....prior to this, you press certain radio buttons in sequence to get codes for unlocking....however, this year started to use the Tech II scanner to unlock it....was the radio working before he replaced it?

Im sure it was working just fine before then he had cds in the changer.