Rigid-Flex PCB Fabrication: Window opening vs slot opening
It looks like the terminology is not yet settled. In this article the groove cutting by a laser refers to the &quot;positive and negative depth control method&quot;.
I think that your slot method based on gluing the finished flex layer to rigid layers. And your window method based on pressing layers all together, followed by
contour milling and window cutting.
It seems that combining separated finished layers is more expencive than joint processing but can be more quality.