Oh that's interesting! I guess I was never explicitly told that A>B>C, it just 'feels' right haha. What you're proposing makes sense too though
Due to this system I have always considered A > B > C, etc.
Some of my children lived under a different regime in elementary school, which common core and non-letter grading assessments. Target, Near Target and Below Target.
A = 1, B = 2 reminds me of cryptography for some reason. That's probably due to reading Neal Stephenson.