Apple apparently has changed that a bit for Sierra. I have the Sierra Public Beta in purchased list (from before Sierra final was released), but Sierra does not show there. In any prior version (from Lion until El Capitan), the initial download is from the App Store product page, but all later downloads come from the Purchased list, including while that version was still current. All of those from Lion to El Capitan still appear in my Purchased list, including the Sierra Public Beta (before release).
Not the current Sierra.
We'll have to wait and see what happens after the next Cat, or Mountain, or Tree, or whatever Apple releases next.
And, I also download current versions of macOS each time the system is updated, stored on an external. I've got all system installers on that drive from Tiger to Sierra, with bootable installer partitions for each. I try to keep those install partitions at the most current version, if I can.