I've discovered that the "new offering" form and the "edit offering" form are two completely separate instances. "new offering" is in the file script_files/php/load_creation_area.php and "edit offering is in the file script_files/php/manage_calendars.php.
They both make calls to the same php and javascript files, so if you make changes in those php or js files you have to make sure the DOM in both forms is compatible with those code changes.
I found this out the hard way when I added a seq_1_detail_subhead and seq_2_detail subhead elements to one of the forms and js code to show and hide them, and of course when the other form invokes the code, js errors are thrown (null objects) and the form elements are not populated.