This list was made using a car on a dyno with an AFR meter to accurately get the corresponding AFR values with voltages.
I have several dynotests with AFR ratio line of several different RS250 with my current mapping (Fastchip Stage 1) and compared those AFR ratio's with my front O2 sensor voltage readout: they seem to be spot on!
I also cross checked with the sensor voltages of my previous Megane II (2.0T) logs with my dyno run together with AFR line, and again it was pretty accurate. It was running a bit lean when I had it mapped due to injectors being maxed out, resulting in an AFR of 12.5:1. My logs show a 0.92V for that.
Installing a seperate AFR meter with a wideband sensor is always better. Even though the narrowband seems pretty accurate, don't trust it too much. Only use it to get a rough estimate of what it is running.