They should be exactly the same, week A should contain letters A thru E, and sometimes F, week B should contain F thru J, or G thru L, etc. depending on how many cars were scheduled to be built, and how many days the plant was working. The actual construcion of any individual car could change by a day or two, since the tags were made up anywhere from a few days to a week prior to actual contruction of the car was scheduled. An individual car could be pulled up, or dropped back in the overall schedule based on parts availability, or the need to get a few more cars of a specific color, or just about any other reason the plant needed, but if it moved up or down it didn't go very far. These changes show up in a VIN shift, in orther words the body number and or w/o number gets out of order with the VINs, since they were assigned at the time the car was actually made, not the time they were originally scheduled to be built. Of course this only applies to the 67's and 68's, as 69's went to a different method of assigning body numbers.