Quote - Aha! So I can have multiple Runtime files, each one located inside a folder I create specifically for a bought item?

Do these new folders need to be arranged in any particular relationship with the Poser folder, or is that irrelevant?

Runtime folders are children of folders you which to add content to and must be linked to Poser to be recognized in the category Library.  There is a particular hierarchy of folders within runtime necessary for content to be separated so that they may appear properly in each Lilbrary category.  You can create these runtimes manually using Poser's main runtime as a guide, or you can have Poser create those folders for you with a few clicks.  Unfortunately, I am not at my own Poser computer right now but I can provide screencaps this evening to illustrate this process.