As far as the C+ goes, the information that the computers use to calculate the PA data is not necessarily the same as what is displayed to the pilot.
That is why the RFM charts are plotted using the information you actually see on the guages.
Specifically, the T5 harness has redundant dual thermocouples. Half of the probes send information to the DECU for power assurance calculations, the other half is used for display of T5 information. A variation in the resistance between the two would cause the computer calculated T5 margin to show a fail but pass when using the displayed T5.
OAT, as mentioned in the previous post, gets carried out 4 decimal places for the computer but gets rounded for display on the panel.
There are a number of other parameters that can affect the computed PA data but what's important and takes precedence is the data the pilot is using to fly the aircraft, hence, paper over 'puter!