Was it common for the date codes to be reverse stamped?
Common? IMHO no but that does not mean they have not been seen that way (individual letters reversed) Worker at the stamping plant just put the number ingot in the die backwards. Thought initially that you meant the complete date was stamped from the other side of the panel.
You will find another one on the lower arm of that assembly that connect to the lower grill & front valance
Trying to decipher the actual date code for my support?
Did you read the article on date coding in the Library? Look under the sheet metal section
In your example we have 3 22 D2 = March 22, Dearborn stamping plant, 2nd shift. There was a change in the lettering usage later in the production year that would not affect this specific piece