Hi Maarten,
I don't have a copy of the manual here, but the IWC perpetual complication have similarities across all models (corrections welcome)...
from an earlier post:
Basically the instruction manual - in particularly the leaflet in red you see below - warns you ((I think that what is says - its been a while since I read it)
a) not to move the time back across midnight;
b) that time keeping on the perpetual calendar only moves forward, and never backwards (though based on earlier discussions I believe the exception is that you can move time back with restriction: which is never to move time back when you are already within, or if it will cause you to be within, the date-change time period of 8 pm to 2 am)
The IWC perpetual calendar controlled by a single crown, with no "quick set" for the date, or "quick adjust" by another name, must be handled very carefully, given its very ingenious and fine engineering.
is the date on your watch overshot ?