Personally, I think that a "complete set" in the OS run (including everything after 1977, such as the 1985 and 1991 series) would be the stickers and the puzzle, since that's all that they had at the time. In everything after 2004, it would be the base stickers, bonus stickers and (if it had them) foil stickers. The seemingly endless variations of the stickers (border variations, background variations, white backs, tan backs, black/red Ludlow backs, etc.) depends on whether or not the collector really wants them.