This article explains how 'show ns event' nscli command is different from 'nsconmsg -d event' output. 

Instructions

The sources of 'show ns event' and 'nsconmsg -d event' with newnslog is different. 

Citrix Netscaler maintains an internal table on memory, which can keep latest 1024 event

Total event list 1024 entries = internal events “not displayed”  +  events displayed in “show ns event” output 

The internal events are filtered out in output “show ns event”.

If the Netscaler is rebooted or 'save config' command is executed, the internal table will be refreshed. 
When displaying event messages regarding services/lb vservers from 'show ns event', the deleted config will be removed from the internal table.