Here some more info from the Chevy parts catalog under the tranny POP codes.
72D30 is similar to the example given 69A372 except yours has only 3 digits for the date.
Whats the build date for the car, very early in the model year or very late? The parts catalog states "The assembly date starts with the first day of the calendar year in 1971 and continues through the 1972 calendar year." Example 372 is Jan 7, 1972 and 30 would be Jan 30, 1971 unless your car was built near the end of the 72 model year, it could be Jan 30, 1972 because the tranny was intended to end up in a 73 model. A bit confusing but things like this happended. I have read that 1972 model year was affected by a stike in 1971 and what new style 73 models were supposed to be out as 1972 models.
The D represents the engine or the vehicle.
D = Mailbu
D = TH400 with 402/240hp (Chevelle and Monte Carlo).
When I mentioned the 350 engine I overlooked the fact that was for a full size car, not a A body.
So it appears like the 72D30 is your tranny code? Since Tom K has a very similar code we can probably rule out a special item.
What do you think ?