My one-sheet for "The Breakfast Club" lacks a Dolby Stereo logo. The film's end credits, just as Mark-P mentioned, also lacks any references to Dolby. Ditto for newspaper promotion. The VHS, Beta and LaserDisc (and I think even the very first DVD) releases all were mono. The DVD & Blu-ray releases that sport a 5.1 track were issued during the re-mixing era; nothing issued these days should be assumed to be the original mix. So...I think the reasonable conclusion is: "The Breakfast Club" was originally mono. (I welcome input to the contrary, though; I've encountered several people that swear it was in Dolby, and this very argument pops up on the forums on a regular basis.)