Why did 1935-on Chryslers products call for ATDC timing?

[Su8overdrive]

Here's something none of us can understand.   We were talking about timing, noting that most immediate prewar US cars had tune up specs showing 2 to 7 degrees BTDC,  other than the 260-ci ohv nine-mained Nash straight eight up to 15 degrees BTDC 1935-37, nine degrees 1938 or '39.   But the point is,   all in MoToR's Manual were and are Before Top Dead Center   e x c e p t   Chrysler products.  

  Why would Chrysler products alone call for tuning specs of  ATDC (after top dead center)?     The laws of physics,  those for four-stroke i.c. engines don't  change.    No other automaker lists anything other than BTDC.    For example,  according to the 1935-42 and 1935-53 MoToR's Manual,  1935-38 Plymouth 4 degrees ATDC, 1939-42 TDC;   1935-36 DeSoto Airflow Six 5 degrees ATDC,  a couple less ATDC 1937-42.   This ends the  War II lower octane gas idea. 

  So our question remains.  In fact, all the more mysterious.   Why just Chrysler of all automakers?

Edited May 12, 2020 by Su8overdrive
clarification (see edit history)

[Fossil]

Miss-print?  Can't think of any other reason. Fuel mileage and performance would go down the tubes. 

Edited May 12, 2020 by Fossil (see edit history)

[Narve N]

Noticed in a Shop Manual (38 or 48, have recently read both) that although the norm was set at ca 2 deg ATDC, you would with higher rating octane (70 or better) be able to advance up to 6 degrees until a slight ping was heard on full throttle.

[Batwing-8]

Could the ATDC numbers represent a static timing value (motor not running)? If a motor is static timed BTDC, you're likely to get a nasty kickback when attempting to start.............