These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Crazy Awesome: The Sleeper Service could do his job because he was acting eccentric, and could act eccentric because he was sort of eccentric from the beginning.
Fridge Logic: The big trick to talking to the Excession is that it only engages in one-on-one private conversations, probably so as not to cause an excession. Which is exactly how any ship in the Culture would act if they were an excession. The Grey Area is the only ship that may have worked this out.
The first Culture ship to report on the Excession mentions attempts to talk with it, which is how it can later be addressed by its callsign, "I". The rest of the Minds involved quickly realize that communication with and studying the thing is less urgent and/or more dangerous than the immediate problem of dealing with how other civilizations will react to finding out about it.