Big Bird neutrino event has announced two different energies: 2.004 PeV, 2.2 PeV. Both values are scattered over web. It may be that the lesser value is for detected "deposited" energy, while the greater value for guessed original/real neutrino energy. I can not find such distinction though. Does anyone know the real reason for having these two values spread over web?
The calibration of large-scale detectors is an on-going process, so reported values can change as improved calibrations become available.
This is especially true for values—like the extreme energy considered here—that lie outside the usual range of usual events.
It is more than likely that after they collected enough of these very high energy events the Monte Carlo was re-tuned followed by a re-tuning of the energy estimator. That would result in a new best fit value for the energy, possibly with tighter error-bars (though sometimes the additional work reveals that the earlier estimate was optimistic and the error bars grow).
If this is the case you can expect it to be reported in one of the follow-up papers.
The best practice is to use the latest available reported values that includes all the data you are interested in.
I was on the calibration team for KamLAND for a bit over four years and we re-jiggered our understanding of the energy scale in that time.