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 points scheduled. Typically (but not always), this is asked for by students who have performed poorly on tests and quizzes, or not completed homework or class assignments. With a failing grade pending, they ask for EC work and points to be added to their grade to bring it up.
EC, as I've defined it, is about points, not about learning. I don't believe slacker students should be rewarded for incomple assignments and classwork. The substitution of EC work for required work just is not fair.
EC is a controversial subject, no right or wrong, and many teachers have strong opinions about it. These are my opinions.
Regards, Barry