I have a couple of these and some $1 coins as well with the same rimming. I've noticed on most of them that they also are a little off centre. My guess (without any technical knowledge) is that the rim die hasn't locked in properly because the planchet wasn't sitting correctly and the planchet has moved a little. And this minute movement has caused the rims to be gouged a little wider.
That's my theory until I hear something better ...
