I was performing a steam sterilization requalification recently. The intended sterilization temperature was 121 deg. C for 20 min. I found that the theoretical temperature was 122,5 deg. C at some point inside the load the temperature was 124,2 deg. C. Basically the conclusion is that the temerature measured inside the load is outside the temperature band of 121 + 3 deg. C. However, in this case I am wonderring whether we are dealing with superheated steam. How do I find out?
In principle people say that the measured temperature should comply with the theoretical temperature to ensure that the sterilization is performed with dry saturated steam. However, what is the margin in which this criteria of conformance is tested. like Ttheor = T meas +/- 1 deg. C ? (or even more?)

An important factor to approve a cycle (requalification) is interpretation of the results.
if the cycle didn't fail at 124.2C, - it means that the control system does not recognize this deviation. May be the controller will abort the cycle at 124.5? A control system that is too accurate may drive you crazy.
The Standard states the allowable accuracy. It does not mention precision or uncertainty. Dont dig too deep.
Why do you think about superheat(1.5 C)? how do you know what is the allowable deviation? I assume that the control system is more "large" than 1.5C.
If you tested Textile pack, could it be Rehydration rather than superheated steam?
there are some (may be many) reasons for such a deviation.

let us know your conclusions
miki