There are quite a few varieties of these beyond the Scott specialized catalog.
The April 1970 issue of the United States Specialist has a lengthy article on this issue. Page 147 notes (talking only about Baltimore, I believe, but see image below of Atlanta): "All printings examined contain constant variations in the Gothic type lettering. The 1st, 3rd and 5th vertical rows of stamps have a comma with a round top, while commas with square tops are found in 2nd and 4th vertical rows. There is a greater distance between the comma and the M of MD on all stamps in the 5th vertical row ..."
The Christmas issue is mentioned in several Specialist articles during 1970.
Here are the same comma differences from Atlanta: