IBM mainframes used to come with documentation in ring binders. Some pages might indeed be marked “This page intentionally blank”. And they would from time to time send out update packages to their customers, with instructions to replace pages so-and-so with the included replacements. On the replacement pages, text that had been altered would be marked with a change bar in the margin.

Lo and behold, one day an update package was received, replacing one completely blank page with one bearing the text “This page intentionally blank”. Complete with a change bar in the margin.