Please fully read the article: Until circa 2017 the administration thought the notebooks were merely misplaced. As it's a tremendously large library that wasn't so difficult to believe, and numerous searches have been conducted over the years to locate the notebooks.

Only after a change of management they investigated the circumstances of the disappearing of the books more closely and came to the conclusion that it's more likely they were stolen.

> Initially librarians thought they might have been put back in the wrong place. "My predecessors genuinely believed they had been misfiled and they would find them," adds Dr Gardner, who became director of library services in 2017.

> There were a number of "intense" searches over the years. They all drew a blank.

So they knew they were missing, they just thought they were misplaced for 20 years.

Confirming that something was lost in a small sized archive, and not just misplaced was hard.

I cannot imagine how much harder it must be for such grand one.