My collecting interest are commemorative stamp booklets and especially the varieties in their cover designs. To explain, below are pictures of two well known examples.
Finland 1992 Remarkable Women has a scarce narrow booklet variation, where stamp pane has been cut short and when the booklet is folded in the middle, cover image fits just and just to the space that is left.
It is unknown why the narrow variation was manufactured. In the back cover of the booklet can be found the exact measures of the booklet in millimeters, and the narrow variation does not fit the description.
Possibly the narrow batch was an error?

France 1970 Red Cross booklet has two variations of the Croix Rouge text. Below is the more scarce 27 mm wide cover text. It would be interesting know why the font was changed. Most of the booklets of this type have 32 mm wide Croix Rouge text.

Is there more examples of accidents or variations like this in commemorative booklets of the world? I leave definitive and vending machine booklets out of my collection because all sorts of cover variations are so commonplace in them.