There is no master document noting the differences (that I know off), but below I created a list of the differences that I know for sure. For the most part the device from a software and hardware perspective does not change. Most of the differences are fixes.
1) "B" and "non-B" are different in mask set numbers, therefore review the new erratas list. Old erratas should be corrected. "B" is 0/1K79X and "non-B" is L91N/L01Y.
2) The Flash & EEPROM reliability characteristics on the "non-B" device is improved compared to the "B" devices. Look at Table A-12 for both device datasheets to see changes to NVM reliability.