Unfortunately, there is no such built-in function in the mIRC client and in IRCd programs, at least I have not seen it.
Most likely you mean some kind of script written by someone else for a client. I am assuming this script is called "Seen" or something. I think this script can still be found on the Internet.
Most often, such scripts are used in bot the "Eggdrop", to track users visits and their actions (for efficiency) on multiple channels at once. But if the user turns out to be quite dodgy and starts changing his nicknames after exiting from all channelss, then tracking these changes will be much more difficult or just impossible. Therefore, in order to fully track users nicknames changes, the bot may need the privileges mode of the IRC network operator, which is not installed everywhere and without special desire for network security reasons. So that, using such a script on your the personal channel without special privileges will bring a small effect of what you wanted to see and may be useless in this case.
Ideally, it would be nice if the developers of IRCd programs would add as an add-on module such a function, with command for request on server. For example: "/WHONICKS" or "/WHATNICKS" <nick|mask> [30d]
Nevertheless, if there is a need to create a new script for the mIRC client with this function, then we can think about it.