I haven't got a '72 I am selling but thought if you haven't found it already that this website may be handy in finding if an offered watch is a '72 or not:
This uses extracts to estimate, pretty accurately, what serial range covers a particular year for Speedmasters. It suggest you need 31.82-32.48m serial for a 1972 145.022-71. This is in fact noticeably lower than the 1972 serials for other Omega models by the way, some of those are in the 34m range for '72 pieces.