The issue is notorious for a weak strike. Much of what you may have interpreted as wear is loss of detail from the weak strike.
IMO anyone who guessed 50 to 55 can consider their guess "correct," since the amount of remaining luster is the main issue in those grades; and luster is very hard to estimate from photos. GIFs are very helpful in that regard. Congrats on the grade!
Wow! AU? Nice surprise indeed. I would have gone no better than 40 but then m grading skills on walkers could stand improvement.