I brought this up at Connect in 2019 and have not seen progress. Assignments flagged as missing are treated as graded. This means that they do not appear in Overdue or Upcoming assignments to students. Once submitted, they do not show up to teachers as new submissions or even re-submitted. So if we mark an assignment missing, teachers and students must manually hunt the gradebook to find them. Please fix this issue as it is one of the major obstacles in getting my colleagues on board with using the Schoology gradebook.
Assignments marked missing should appear on a student's to-do list (upcoming, overdue, whatever it is). Once submitted, a new submission or re-submitted assignment should appear to teachers.