M&P revolvers were generally offered with two alternative calibers: .38 and 32-20. The earliest offering of a 2" barrel occurs in the 1935-1936 catalogs, which show barrel lengths of 2", 4", 5", and 6" lengths for the .38 round-butt M&P. In the 1940 flyer, the 2" length is available for the.38 square-butt M&P as well. There is no offering for the 32-20 caliber option.
The earliest 2" revolver I've owned is sn 614221, a .38 M&P, shipped Jan 1935.
Production for the 32-20 caliber had ceased a good 10 years earier. It's worth noting that 32-20 caiber option involved a different barrel bore, and a different cylinder chambering. Otherwise the 38's and 32-20's guns are identical.
Given all of this, it's unlikely that the factory ever offered a M&P chambered in 32-20. By the time the 2" barrels were first offered, the 32-20 caliber option was no longer available.
Regards, Mike Priwer