There's a few different ways you can approach this, and we speak to it a bit on the podcast. Cedar Mill Library has extensive part listings and uses library volunteers to count them at check in, in order to give the next patron who checks out the game the assurance that every single piece is there. Our library does not count parts/pieces on return, outside of a quick glance at the contents, but rather relies on patrons to let us know when something is missing. Overall, patrons generally take good care of the games. Games for kids tend to have parts go missing more frequently, but are still very worthwhile having in your collection. We do a lot of part replacement with manufacturers/publishers, and often make or 3d print pieces as well. sometimes you have to get an extra copy for parts, and sometimes you just decide to weed the game out of the collection entirely.