Does Powerconnect 5224 have private SNMP variables that count packet drops?

Hi!

[rmon.statistic.etherStatsTable.etherStatsEntry.etherStatsDropEvents] is a SNMP variable for counting drop events. However, When I made a situation that essentially generate packet drops (by sending excessive traffic), that counter(i.e., etherStatsDropEvents) have not increased at all. Is it correctly implemented in Powerconnect 5224? Or, do you have other SNMP variables to detect packet losses in Powerconnect 5224? Thank you in advance.