Looking at quest script, early completion was granted because you satisfied S.02 first (click questor with true letter) then dropped letter later to satisfy S.03.
One way to hack in a fix for this is to start a "pc at _inn_ set _clearclick_" action in the startup task. Then decouple the questor click to its own variable you can set/clear like in CUSTOM01.
This way as soon as player enters the target inn a second time, the _clearclick_ task will trigger and clear the questor click var before player can drop letter. Then they must return to questor as normal and click them again.
Probably other ways to do this, but that was the first thing that came to mind.
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