Apple uses hexadecimal for it's versioning so in this case:
B20 is the newer of the two.
Since Mavericks Apple has moved to updating the firmware when needed via the OS installer. So its possible your OS version you are currently are running did not update it to the newest version. As an example if you upgraded your OS to Sierra your firmware should get updated if it was needed (not all systems get the newest firmware).
Here is an Apple T/N that goes over the baseline firmware versions: About EFI and SMC firmware updates for Intel-based Mac computers.
So in the case of my own MacBook Pro system which is presently running El Capitan my Boot ROM is MBP81.0047.B2D (2861) yet what is published is MBP81.0047.2AB (683). So you can see my running version is newer than what the TN lists! Most of the newer firmware updates are related to security issues Vs hardware fixes.