In the Boeing Manuals "residual rate of climb" means the climb rate achievable when you reach that altitude. If for example you can still achieve 300 fpm at FL350 but only 290 fpm at FL360, then the maximum altitude would be FL350.
Generally there can be differences between the QRH altitudes and the FMC due to a varience in the inputs.
Old_smokey, welcome back....
We are just moving back into the Airbus world, so your explanation is interesting and appreciated.
Mutt