So what exactly is the question? If SteamDB lists two bundles, and you're getting the smaller one, then you're getting the smaller one.

You can only know for sure by redeeming the key, since there's no way for users to determine anything about a given key. However, if even the seller says it's the smaller bundle... although he could still be lying and the key isn't that bundle at all.

You get what you get that the dev put under the key license for, it doesn't change, the dev can change what in the bundle.

If key is for duluxe edition, you get what comes with duluxe edition.

If store selling GOTY edition, people get what they buy from GOTY edition.

If game dev only rename duluxe edition, and getting same things then you're getting same things nothing to overthink about.

If game dev created two bundles called duluxe edition, you can see this from steamdb.info to see the difference between the two, and take an educated guess which bundle key for, as likely getting older bundle than the new one, so safe to assume if getting the lesser/greater bundle. Sometimes devs make bundles giving more DLC such as pre orders included, or not getting newly added DLC in the newer bundle. Note like I said if both are same DLCs no extra, or less then getting same thing.