According to StalloneZone, Stallone confirmed that the poster released last week was unofficial! The official poster is far from being complete and won’t be out for several months.
I still believe that the poster was made by someone who had access to pictures taken on the set. The poster was either leaked inadvertently, or on purpose to gauge fans reactions. The other option could be that someone got a hold of some set photos and had the poster made using those.
We'll find out depending on whether the final version of the official poster will end up looking like this: