+1 to Jeff's comments
In addition, (H6) is the date the body was bucked. The buck tag date usually is close but does not match the door data plate date. Also, the buck tag date is in reverse order compared to the date on the door data plate. Second year of production codes were not used on buck tags, so if a Mustang was built in August of 1965, the door tag used the letter "V" for the month, but the buck tag used the letter "H".
Regards,
Ron