Difference between PDA MI3 and NB1
These codes are just Samsung's own version codes, and as far as I know, they have no logic, except that they increase alphabetically and numerically with each new release. You'll have to either install and check the version they correspond to, or search for news of new firmware releases for your device to see what they upgrade.

As for the PDA/Phone/CSC, PDA is the OS itself, Phone means the Radio firmware (GSM/CDMA/UMTS/LTE radio chip) and CSC stands for Country Specific Customization (or Carrier Specific Customization), which provides regional customizations such as carrier APNs, available languages etc.