Mintmark Varieties Die Varieties

Working on the quarter book has proven to be the most knowledge gaining experience of my 2 year old coin hobby.. Using the CPG and with the help of our the CCF people I have gained some awesome knowledge and places to get more knowledge!! Special thanks to Coop who I am sure has had to endure some real hair pulling emails!! I am just intrigued by the many mintmark varieties of the Washington quarters seems to have calmed down in 1964 with the 64d reverse of 65. I was wondering who else chases these coins? Altho according to the CPG they had mixed up dies until the early 70's. These coins have become a passion. This is my 64d 65 reverse
Edited the title due to it being vague toward the subject of thread more or less a last years dies or inadvertant mint marks and just plain strange die variations from one year to next