This is an event counter for how many times a packet was dropped on this interface due to a lack of switch resources, rather than a count of the individual packets themselves. Because DropEvents undercounts the true number of discarded frames -- RMON's etherStatsDropEvents semantics mean one event can correspond to many lost packets -- even a small non-zero value for this completed, frozen 24-hour historical bin on this port is a stronger red flag than the same-sized bump in a plain packet counter would be. For example, this completed 24-hour bin showing 40 drop events alongside a rising InDiscards count on the same port points at sustained buffer exhaustion on this interface, not a one-off blip.