My guess is that the film was matted anywhere from 1.66-1.85 in theaters depending on the country it was shown in at the time. Weir seems to prefer 1.77, as the Director's Cut of Picnic at Hanging Rock was made specifically for the Criterion release in 1998, and the DVD at that time was released 1.77 (though non-anamorphic), with a limited theatrical run at the time as well.
Would be interesting to see if there's any documentation specific to the film. Could be a Barry Lyndon-like situation.
Edited by Brandon Conway, March 18 2014 - 09:05 AM.