What’s the meaning of the underlined issue?

What’s the meaning of the underlined issue?

The passage below is from The Library: A Fragile History by Andrew Pettegree.

Paperbacks posed yet another problem for public libraries, as they were smart enough to be collectable for the home library, but not sufficiently resilient for repeated reading. None of these challenges proved terminal. In the financial year 1961–2, public libraries in the UK spent £6 million on new books, a creditable increase of 10 per cent on the previous year. This represented 9.8 per cent

of total domestic book sales. The previous year libraries had recorded 441 million issues, from a total stock of 75 million volumes, an increase of 25 per cent over the past ten years.

For the life of me, I cannot pinpoint the meaning of the underlined ‘issue’ in this context.

In 1961 libraries in the UK recorded a total stock of 75 million volumes.

Right. Libraries in the UK has those number of books at that time.

But 441 million issues? What this number refers to I cannot figure out.

Thanks in advance.