You can find out if events discarding is happening on the ProxyPushSupplier for example:

struct ProxySupplierInfo
{
   unsigned long queue_size;
   unsigned long total_retries;
   unsigned long current_retries;
   unsigned long discards;                  //<<< We're interested in this
   unsigned long event_counter;
   ProxyState state;
   Object client;
};

interface IT_ProxySupplier // Root of all proxy suppliers, so in push pull etc
{
   readonly attribute ProxyType proxy_type;
   readonly attribute string proxy_name;
   readonly attribute ProxySupplierInfo proxy_info;    //<< here it is
};