BABN which included commemorative stamps Scott #482, 483, 484 & 490. During this time these stamps were issued with a perforation of 10. Most commemoratives of this era are perf. 12 stamps.
Many of these BABN experimental stamps have one or more straight edges as if they were booklet stamps (they were not). If one finds an example of these experimental printings which have sound perforations on all four sides it generally sells at a premium over those with one or more straight edges.
Below are three examples I've found of Scott #490, the "Curling" commemorative, showing perforations on all four sides, straight edge on one side and straight edge at the top.
A collection of these stamps can be formed which includes an example of each possible configuration. The stamps occur with not only with a single straight edge but with two straight edges as well. The 2010 Unitrade Catalog explains the reason for this difference:
Panes produced with inscriptions (philatelic stock) will have one side of the pane without selvedge (i.e. a straight edged stamp); panes produced without inscriptions (field stock) will have a straight edge on three sides of the pane (p. 170)
Therefore, for each stamp there exists a fully perforated example, four different single straight edge examples, one for each side, and the potential for examples with two straight edges one from each of these positions in the pane: UL, UR, LL, LR - depending on which side of the pane had selvedge.
If you have any experience collecting these BABN experimentals I'd love to hear from you! Leave a comment and let me know how you've collected these.