Are Foldouts Always Shorter to Left but Longer to Right?

[-JKP-]

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So here’s my question: Is this phenomenon just a coincidence, or a common practice at that time? In other words, is it possible for the original author to design pages that to be bound in a way where left foldout is longer than right foldout?
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I don't know if it is coincidence or common practice because I don't see many manuscripts with foldouts, but having a longer right-side foldout might be more convenient for a right-handed person.