As mentioned, mentors can review submitted proposals before the deadline after they don't have to.
Since the GSCO portal does not support any kind of review support/discussion about reviews, the related mentor(s) might get in touch with you. But as said: there is no official obligation of mentors to review proposals before the official submission. For my own topic, I already reviewed four proposals and asked for clarifications and asked for more specific statements regarding the topic and the depth of information provided.