My claimed MER was definitely a stretch. I shoot that distance and further a few times a year, and I was overconfident due to a recent successful outing. I’ll definitely be incorporating some more constructive practice.
I genuinely think that the most beneficial thing that's happened in the last few years was my miss on my first 600 yard qualifier last year. I had spent lots of time on kids' rifles, kids' practice, and almost none on my own that spring.
It's a much more perishable skill than we would like to believe. In hindsight, I'm glad I didn't luck my way into hitting that shot, it was a wake up call that long range proficiency is not a one way ratchet, but a skill that must be maintained.
Don't hang your head, a couple of near misses cold bore from 500 yards is better than the vast majority of western hunters would be able to do!