M-20 decoding questions

[69rsss350]

My 69 RS/SS 350 vin is 124379N671780 build date 08C
tranny # is P9H20A which would indicate a 6/20/69 build date for the M-20. Is it more likely that the "H" is correct or am I misreading what could be an "M" which would make the build date on the M-20 8/20/69. Is it common for the tranny to be approx. 2 months ahead of the cars build date? Casting # on tranny is 3925660, bell housing 389962. There are also some smaller vertical numbers aft of the larger P9H20A, what are these for? Thanks in advance!