It can't be a broken letter on an edge die, a quarter has a reeded edge, not lettered. Just damage as stated.
Take some time and think this through. Which design element on the reverse has the same size and shape of the mark on your coin? Why is there 1 bold mark but no other adjacent design elements along the rim? How is it possible for a die strike to leave displaced metal? To paraphrase tge 14th century Franciscan monk and philosopher William of Ockham - the simplest explanation is usually the correct explanation. Do you think it could be PMD from a hit?
http://www.error-ref.com/rim-restricted-second-strikes/ Here's a site that explains rim restricted second strike it explains what I think happen to this coin
Based on what you've read in error-ref, how can the mark on the rim be a different size and shape from anything on the die? If it was due to the die bouncing the lightly striking the rim, why is the mark bold, yet there are no other design elements adjacent to it? Go back and review the pics on error-ref.com
I'm new to all this and I think it is PMD. The site you referenced all have the "rim-restricted second strikes" in the same plane as either the obverse or reverse of the coins involved. The picture you have has the strike directly to the edge of the coin, albeit nearer the reverse of the coin. Just my thought on the matter.
From 1996 through January 2011 edge lettering was used at the Philadelphia mint its possible this is how the D got onto the edge could of been a possible mint error there
Not possible. Edge lettering was not used on quarters. This can only happen on coins with edge lettering such as the presidential dollars.
I thought the 2007 Presidential Dollars were the first modern coin to use edge lettering. Where did you read from 1996 ? ==> https://atlantagoldandcoin.com/edge-lettering-in-u-s-coinage/#:~:text=Several types of U.S. coins,and half-dollars in 1794. ==> http://www.smalldollars.com/dollar/page33.html