Are Foldouts Always Shorter to Left but Longer to Right?

[nablator]

Oops!
The Grove comment was not from the interlinear file but from the old mailing list.
I can't link to posts from there, so here's a screenshot:

Since f. 67 was not a foldout originally, the most likely original number of foldouts would be 10, right? (Not counting possible foldouts in missing pages of course.)
68
70
72
85
86
89
90
95
101
102