I just wanted to chime in that, alas, I can't even guesstimate a date. But I want to add that copyright dates can be very misleading. Compilation VHSs are usually copyrighted as a separate assembly, so that (for example) Xavier will take a loop from 1973, 75, 77, etc., hook them all together, and copyright the whole thing as of 1985, or whenever they assembled it.
All you can be certain of is that none of the film was shot after the copyright date.