According to the IMDS user manual (ver 10.0), when releasing a Material MDS, the user must confirm that all GADSL substances in his/her MDS are declared by selecting a check box "I have declared all GADSL substances" (please see attached print-screen).
In other words, the supplier of your raw materials is obligated to declare (and not hide) all declarable and prohibited substances.
Thus, "compliance to GADSL" should be understood.
Alex.