The answer is that no engine set is matched at all, and the change in operating conditions between a powered condition and an idle one is enormous. Slight differences in blade tip clearances, bleed valve port sizings and valve openings, etc. all contribute.
A digital gage is the real culpret, where one can read to the degree, one expects similar consistency in every way. Actually, most T5 gage systems are not good for more than about 5 to 10 degree accuracy.