Trim surface

I'm having trouble with a certain grasshopper proces involving trimming surfaces.

The basic setup of the scripts is to trim a given surface into smaller "panels" between given corner points. Plates can also have different pieces of different surfaces. And that is where it becomes tricky. 

I've written a script which calculates the contours of the plate (green pipe in picture) (1 list of different curves, ON one of both surfaces shown.) The problem is when i just plug in the contour data to trim 1 surface, the curves of the contour which are not on the surface also have an influence on the trimmed surface. How i can avoid this ?

To make it clear I want every surface trimmed seperately, so no joining the given surfaces and then trimming the whole.

To clarify the picture: the purple surfaces are given (a corner), the green pipe is the contour data (they join perfectly and are projected on the surface). The red-ish surface which you can see through the purple surface are the trimmed surfaces. As you can see the trimmed surface is over-trimmed at the top. The same goes for the upper surfaces.

I can fix the problem by manually selecting the contour lines which are adjacent to the surface. but this takes in to much time and I'm searching for something automated for different alike procedures.

Thanks in advance.