It would be nice to have a "Displaynames with OLD NAMES" option in the show names pull down in the General tab of preferences. It is true we have something close with "Displaynames with username" but that does not show "Resident" So Joesmoe Resident is only Joesmoe. While not a big deal for some, if you are doing a log search you can be more specific and reduce false positives if "Resident" is there.
In the modern chat logger, Resident gets culled before the username ever reaches the log or the display, there is the option to display Resident LiruShowLastNameResident, you could try that.
Of course it creates a new log file. But we can rename the old, or copy it's contents to the new.
@OP - You can either use the debug as Liru suggested or in prefs, it is Show Resident on the General tab