This would take the manuscript and a ruler to check, but to me it looks like the original folds were intended roughly at the normal folio width from the gutter. For this to work the odd-sized foldouts had to be neatly and carefully folded after each use. However, at some point someone just folded them carelessly wrong and then left the manuscript shut for years or decades, and the new folds became permanent.
Edit: turns out I somehow skipped over the part where you said essentially the same thing.
Edit: turns out I somehow skipped over the part where you said essentially the same thing.