Thanks for sharing that link, KRivers. I recently bought a Mac Book Pro which came preinstalled with macOS Sierra 10.12.6 but thought I couldn't download it since High Sierra was already out on the App Store.
In fact, Sierra or High Sierra doesn't show up on my App Store purchased list (see attached screenshot) like it does with El Capitan, Yosemite, etc. even though I've already downloaded both.
Is this right? Do others have the same issue?