He's what happened with me so far.
Hypermode event If you played via galaxy, the hypermode event was enable. You could see the counter of zombies killed and your hand to hand damage was set to hypermode.
After reading that the bonus weapons would come via dockets I contacted Techland support.
They said Dockets are only available via Steam, Xbox Live and PSN. I assume because these platforms have a social API that lets you link your account to their services (like we can link Steam account to GoG Connect)
A little miffed, but DRM free sometimes comes with down sides.
Except, at the end of the promo I got 2 dockets. Then a third a day later.
My son that also uses my copy on his machine got a second set of 3 dockets too.
I updated my ticket, but got no reply.
Ye Olde Trusty Again seeing this was Docket based I asked support
Hi Guys, I've got Dying Light Via GoG. I've been able to get the Military Rifle via a GoG key, but you are using dockets for Ye Old Trusty and GoG doesn'ty yet support these. Will you be making a GoG key or will there be any way to link GoG accounts? Vince
Their reply
Dear Mechmouse,
Most likely we will, though no further information on the matter is available at the moment.
Make sure to subscribe to our newsletter at gemly.com (at the bottom of the page) and FB profile to obtain the latest news and updates as soon as they are revealed by our teams, please.
Best Regards
Techland Support Team