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I have a 12/2018 build and just got that update a few days ago. Your car is up to date. Even when there is a newer update, not everyone gets it at the same time.
It doesnt "notifiy for any software update" because tesla has not flagged your car for any new updates yet. The car will tell you when there is an update ready for you to download, and there is nothing (zip, nada, zilch) that you can do to speed that up. the only exception to that is, if you go a couple months without an update and there are several that come out, you can contact tesla via an appointment in the app to ask them to check your car to see if any updates are available for it.
TL ; DR
you just need to wait. The car will tell you when it has an update for you, and nothing you will do will speed that up.