You are correct that a drop is not unusual and aeh already provided a really good explanation of why. At the same time, neither rising scores nor stable scores are unusual either and that is why the "percentile calibration" are the same. DS & DD, who took the 6+ version for the first time last year, are instances of stable and/or rising scores, but they also scored at the top of the charts. For what it is worth, DS/DD concur that the 6+ tests were harder, especially for DS, who scored substantially above the 99 percentile threshold.
