Threshold
The ruler hides every earthquake weaker than the magnitude it names. Bars show earthquakes per year at that threshold; drag across them to pick a range of years.
Hatched bars and Mc
Each era's station network had a floor - the magnitude of completeness, Mc - below which it could not hear. A hatched bar sits below its era's Mc, so that year is incomplete and says more about the stations than about the island. Raise the threshold above every Mc and the years become comparable.
1999
One sequence makes the year: 342 of its 719 earthquakes came in August, aftershocks of the M 5.2 of 11 August near Limassol.
What this does not check
Part of the remaining difference between eras may still be instrumental - the b-value drops even at a single threshold, and this version does not test it.