I traded a working IBM 5150 with 64KB-256KB CPU for an earlier (but not working) 16KB-64KB CPU Model.
This is a 10/1981 model, without the IBM-labeled disk drives. I have not yet confirmed that IBM sold systems with non-labeled drives, or whether these were added by the reseller to save money. The date stamp on the IC's of the drives range from 1980-2nd week of 1982, and one could theorize that the drives were added later, after market. That explains why they're not "IBM" labeled. Just my hunch.
I swapped out a working 16KB-64KB CPU board and brought the system back to life. The drives work, I did not test the CGA card that also came with it. The previous owner had both a monochrome and CGA card installed, which may have caused the motherboard to short out. Not sure.