It’s not an excuse if the parent sends it in. It has to be signed by a doctor.
I managed to get a blanket excuse for my son’s migraines - a letter from his doctor that says he has them and their rough frequency.
Some districts would want my son to see the doctor every time he had a migraine. Why? It’s completely subjective unless you put him in a CT scanner, and the doctor can’t fix it any better than the medication already prescribed.
Same thing with viruses and fevers - some districts you’re supposed to drag your child to the doctor, infect the other patients in the waiting room, make your child miserable, and get told,”It’s a virus, he’ll be better in a few days. Here’s an absence note.”
Same with some jobs.
If the school administration had any common sense, any compassion, any decency, any honor, they’d waive the requirement in an instant - what does the word “guideline” mean, anyway?
Some large companies have migrated to the concept of Flexible Time Off (FTO.) In essence it is an earnable vacation time that you can take whenever you need it. You can take it also in case of short term medical problems. Long term medical is a different story.
Petty tyrants only have power over this guy because he wants something that they control. I certainly wouldn't beg them for anything; but this guy's circumstances may be different.
Myself, I never set foot to a graduation ceremony of any kind. I hate such things. The teacher was really confused when I said that I have important things to do instead :-) (like the tuning of my 80 meter dipole on the roof, as I recall.) I also remember picking up my university diploma at the secretary's desk. Easy, quick and convenient. The end result is the same. Skip the fluff, do things that matter instead.