Therefore it can be deduced that RT conforms to the L*a*b* standard.
Thanks for the feedback. When I quickly compared L*a*b* values between Photoshop and RawTherapee yesterday, I found differences I could not immediately explain, so I wasn't sure what to think of that (probably caused by a missing profile assignment). Otherwise I could have confirmed your finding already, so I had to find a bit more time to delve into the matter. You beat me to it.
Photoshop of course doesn't display a* and b* readouts beyond the [-128, 128] range, but other than that things seem to look similar.