Does anyone know whether it is in accordance with the rules of technology if the guide rail of the roller shutters does not extend to the window sill?
In our current house it looks like this, as seen in picture. To my mind, this is one clean job and the other botched. Of course, I could be wrong.
Yes, there is a DIN that writes something about 8 mm. Basically metal always needs some air to expand.
As I understand it: ...it is often installed in such a way that the guide rail rests on the window sill rail (as seen in your case) and this is also _not supposed to be wrong_, because it can be ensured that the window sill is easier to clean. From a thermal point of view, this gap is not relevant.
Corinthians pull themselves up by the 8mm and then may be annoyed later that dirt spots form on their window sills because they cannot clean under the smaller/equal 8mm. That is the difference between theory and practice! This is my layman's half-knowledge on this subject.
I'm not an expert, but the design in the old house seems better to me. In my house (not new construction) it is also the case that the shutter guide rails end just before the window sills (as in your right picture). As in the left picture, I would be worried that the last slat of the shutters might be at the bottom. Some air is necessary in my opinion (water drainage, expansion in heat), but not more than 5 – 10 mm. I can't estimate it well from the photo, but I think it's more in your case (2-3 cm?).
Looking around the house here, that's quite normal for metal window sills.
Here they are all like that too and stop about 1.5 cm before the window sill. Has nothing at all to do with botching in my understanding.