Multisite and library versions

Multiple sites running from the same Drupal core can have different versions of the same app (and not see eachothers' apps), as long as I set the apps path to sites/%sitename%/modules

But since the library path is hardcoded to sites/all, they have to share the same library. So if those different app versions have different versions of the same library, they will conflict. I'm unsure if whichever app installs last "wins" or if the highest version of the library "wins" but both are potentially site-breaking bugs if my apps require a specific library version.