More than that, I would guess that they will defend themselves with an argument like the following.
They will claim that they are lending out copies of books locked up in other libraries. And there are librarians from said libraries willing to testify that they have agreed to allow this. They have ceased tracking inventory because getting a detailed inventory under current conditions is challenging. But they believe that the number of copies that they have available exceeds the number that will get lent.
If challenged, they will have the number of book X lent out on file. As long as they can find more libraries willing to say "We authorize them to lend the copy we can't lend physically because of quarantine" than they lent copies, this argument has a shot.
They will claim that they are lending out copies of books locked up in other libraries. And there are librarians from said libraries willing to testify that they have agreed to allow this. They have ceased tracking inventory because getting a detailed inventory under current conditions is challenging. But they believe that the number of copies that they have available exceeds the number that will get lent.
If challenged, they will have the number of book X lent out on file. As long as they can find more libraries willing to say "We authorize them to lend the copy we can't lend physically because of quarantine" than they lent copies, this argument has a shot.