Ensure that products per page is consistent

Woocommerce Version 3.0.7

I found and followed the directions here:
https://docs.woocommerce.com/document/change-number-of-products-displayed-per-page/

// Display 24 products per page. Goes in functions.php
add_filter( 'loop_shop_per_page', create_function( '$cols', 'return 24;' ), 20 );

It works, almost.

The site where I’m using it has a lot of sold out items. It seems like the sold out items are counted in the loop, leaving fewer than expected to display on the page.

I’m looking for a way to consistently display the chosen number of items per page, except of course the last page.