MIA For Most Carriers
While the Samsung Galaxy Note 5 is confirmed for T-Mobile in the U.S., it's missing in action for most carriers around the world.
We've seen several carriers issue Android software upgrade updates and none of them feature the Galaxy Note 5 Marshmallow update. Rogers (Canada), Vodafone (Australia), Optus (Australia), and Telstra (Australia). None of them include details about Galaxy Note 5 Marshmallow updates.
So just because the Galaxy Note 5 Marshmallow might (and we stress might) roll out in December doesn't mean it will roll out to everyone. These roll outs take time and it'll probably stretch over the course of several months.