Many years ago I attended the College of William and Mary. At that time the standard in their English department was a failing grade if a paper contained a single grammatical mistake; including spelling, punctuation etc ...and this was before the days of PC's and spell-check. Subsequently, I had to work very hard to get a solid B; but, I learned more from that experience than from any other course that I have ever taken.
Your grammatical background dropped my jaw. If I had known last night what I know now, I’d have bit my tongue and slunk off into the night. ;)