Hi Sharon:
You've presented a very clear guideline that works for you and your institution. I think we might be taliking apples and oranges.
Make up of missed work due to wahtever, to me, is not extra credit (EC), and I do not favor the awarding of EC in general. Of course, there are circumstances where accepting missed work will be necessary, and I agree there should be clear policies about this at the outset.
I think of EC as doing something extra, beyond what is called for in the curriculum to earn extra points above and beyond the total… >>>