Can you help me read this date code for a tire?

[71 RT]

I understand how to read date codes for fairly recent tires, but I have one that has this stamped in it.  See pic below, all letters and no numbers.
Anyone have a clue as to what these letters mean?  It is on a GoodYear Polyglass g-60-15 raised white letter.  I was told it might be original spare out of my 71 Charger, but not sure.

[hemigeno]

Based on the deciphering info from Greg Kwiatkowski (printed in the back of Galen's little white book), here's what the code means:

BA = 31st week of 1970 (which means July 26th thru August 1st)
NB = Akron Plant II - Akron, Ohio

Very easily could be your original spare if you have an early-built 1971 Charger.

Pretty cool...

[71 RT]

Thanks for the help Hemigeno!  Yes I do have a rather early production 1971 R/T.  The fender tag said the date of construction was August 18, 1970.  I have been told it was during the second week of production, but I can't confirm exactly what day they started building B-bodies in Lynch Road.  Thanks for the information, looks like the guy might have been telling the truth!