Well Andrew, you could perhaps agree that the accompaning text is a failure. How many times have we had this question?
Imagine the accompaning text was true instead of false. I.e. that it did not claim he appeared in Terra incognita where in principle no army of a player can be (although one exception to this exists, but that is of only academical interest just now)
The accompaning text should be something more true and more easy to interpret. It appears quite simple to achieve. I will give an example of how to change the code. Today it may look like this
If province ID is blank then display "Leader X awaits your command in TI"
else display "Leader X awaits your command in PROVINCENAME"
Change that to
If province ID is blank then display ""Leader X awaits your command on board one of your fleets"
else display "Leader X awaits your command in PROVINCENAME"
Since the location of the fleet is known to the programmer as well, it is the ID of the Sea zone where the fleet presently are, and most Sea zones have a name you could even give that name in case it exists.
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Indeed, now and then even experienced players get irritated by this message. Not because they do not understand the leader spawned on a fleet. But because it may take "long" time to find out on which fleet he is.