It's based on community-/author-provided static lists (the -seconly.txt lists). An automatic determinion isn't possible, as the catalog contains both the full and seconly rollups, and both are of the "Critical" category.
While you can keep using 10.9, it's recommended to update to later versions because of improvements, bugfixes and potential new features. Additionally, a change in the list format could (in theory) render all older versions inoperable. Last but not least, MS changes links all the time and with old versions you need to take care of the lists by yourself.
tl;dr: The lists are community-based and verified. Update is recommended but not required.
Microsoft update catalog: http://catalog.update.microsoft.com/v7/site/
Windows Install media creator: https://support.microsoft.com/en-us/help/15088/windows-create-installation-media