> What Canvas refers to as a 'Course' is, in our institution, the overall award (in our institution a Canvas Course reflects a unit of delivery we call a Module), so the student who sees the nomenclature 'Course Grade' may misconstrue this to represent their cumulative Grade, GPA or overall award classification.
If you redesign your Canvas so a course in Canvas matches what you call a course, it will be easier for the students to understand.
> The student may have incurred a sliding scale penalty for late submission, which we calculate outside of Canvas
Canvas allows you to set late submission penalties in Canvas. Alternately you can adjust the grade manually and enter an explanation in the Notes field.
If you do not enter the grades into Canvas correctly, the average will be wrong as well.
> The student may be submitting a capped reassessment, where the penalty cap will be applied outside of Canvas and may limit the work to a passing grade (some reassessment students may be resubmitting without penalty)
You can manually adjust the grade in Canvas.
> An assessment may be a zero credit "read and sign" type activity which we may need to set as a 'complete/incomplete' grade - however this seems to require a points value and would then modulate the grade and be included in the Canvas Course Grade
> An assessment may be a zero credit pass/fail element which must be passed (sometimes for an external body 'fitness to practice' check) at a level above the passing grade for the unit or delivery or award (eg 40% for the academic award, 75% for the fitness to practice assessment) - again seems to require a points value
You can set grading categories. I almost always have a category for "Not counted in grade" that counts for 0% of the grade. This can be done under "Assignments."
> Whilst Canvas checkbox 'do not count this assignment for grading' may offer a partial solution path, this requires that we are able to guarantee that all colleagues use this correctly
Ensuring faculty compliance might take several steps:
1. Figure out how to make it work, and double-check that that really works.
2. Write up how to make it work in clear terms, using screenshots. Maybe also record a video.
3. Send your write-up and/or video to all affected faculty.
4. If you are an administrator, check in on their courses. If you are a teacher, either sit down with them 1-on-1 to check, or ask them to add you as an instructor so you can verify that they have it right.
I hope this helps, and I apologize for my Texan. (I dare not call it English.)