You say there is nothing not to trust about the Grade system?
Having been to Japan since 1975 has taught me sociologically, theologically, culturally and philosophically that the Japanese males abide and live by structure, discipline, ordered roles, yang concepts and ethics passed down by Taoist- style traditions. The Grade system should be a trustworthy structure according to the above; but it isn't!
Cars that appear in Osaka that have come from as far north as Hokkaido has happened before - and will happen again.
I don't doubt your experience; but anyone who trusts the Grade system only can still (without precautionary backups) end up with the rusty car.
JDM_Performance once bought one from Northshore Prestige - with regret from a faulty Grade system.
Aggroman once bought one from Top Secret Imports - again with regret from a faulty Grade system.
Therefore, I say to you that the Grade system isn't the only criterion to abide by!