Was the 21-fold 9th the infamous "squabble pack" by any chance?
It was indeed!
It's interesting that the 21-fold green wrappers with the group of 3 ads (Initial, Jade, Wall Poster '74) seem relatively common, and yet
these wrappers were only used for the 9th and 11th series, for which the 21-fold unopened packs are somewhat to very hard to locate.
I guess what unopened material is readily available is just a fluke as to what turned up as unopened. The 21-fold 9ths must have been
common at the time, but just weren't part of any finds of unopened material, whereas the 85-fold 9ths and 10ths are all over the place
in unopened form.