just pulled the Amherst Coop data... For those Decembers you mention they report 18.8, 17.6, 24.2, and 26.6 respectively. Granted the Amherst Coop hasn't done quite as well as MBY this year, so that 1970 number might edge it out at present, or is close. (edit- always the possibility of missing data, but no indication thereof)