Crucially, AFAIK digital lending systems aren't based on the number of physical copies a library owns; they're separate licenses. Thus, in a scenario where a physical library is closed but digital lending is still available, a significant portion of the library's catalog is inaccessible. At least in this regard, IA's logic is sound: practically-speaking, the number of copies of a given book that they lent during the period in question almost certainly never exceeded the number of copies held by closed libraries in the US.