On board diagnostics regarding European cars can be a little tricky, and I am going on experience here... Even though there is supposed to be a common communication protocol between the scan tool and the vehicle, it is entirely possible that the car is working fine, but there is a glitch in the scanner software that is causing the rear O2 sensor to read zero.
With the scan tool you have, you are somewhat limited... and honestly, you may need to take a trip to the Volvo dealer if you want to make sure the readiness tests have run.
I feel your frustration trying to pass CA emissions... but I don't know of another way around this... Obd II is complicated, and without boring you with unnecessary details, it is a progressive diagnostic system. As an example, the front O2 sensor must pass a heater test and then an operation test. Next, the rear O2 sensor must pass the same tests. But there is very specific criteria for these on board tests, and the vehicle has to be operated in a certain manner for the test to run. I looked up the code you supplied, and guess what? There was no information as to what it takes for that rear O2 sensor diagnosis to run! AGGGGHHHH!
Moving along, once the oxygen sensors tests have run and passed, then the catalyst diagnostic needs to happen - catalyst efficiency... and so you see it takes a while for the car to run its diagnostics and set the Readiness Monitors.