WT_STAT_USECS_HIST_INCR_FUNC only increments for lt1000 and lt10000, so for example if a data point is 2000, it will be counted as lt10000. This means that if we defined buckets like lt2500 (e.g. here),  2000 will fall into the lt10000 bucket instead of lt2500, which is incorrect and cause confusion when looking at FTDC.