Yes sources on this are notoriously difficult, especially since the use of apprentices was an open secret. I did find this source which talked about Rubens and

Yes sources on this are notoriously difficult, especially since the use of apprentices was an open secret. I did find this source which talked about Rubens and Rembrandt: "The structure of the work was usually as following: Rubens sketched and corrected the painting at the very end, and his "staff" was given the whole main stage. To increase the speed and efficiency of work, Rubens shared the duties: some of the pupils painted the background, others were focused on details — they worked on foliage or clothing, the master himself corrected the whole work and execute the most "important" parts — hands and faces." Link: https://arthive.com/publications/2854~Rembrandt_the_teacher_stories_about_the_arrangement_of_the_artists_workshop_and_his_five_pupils https://arthive.com/publications/2854~Rembrandt_the_teacher_...