Hirako__: Actually its possible during these giveaways to see a key redemeed by multiple people but only the first one will get it. Even I have seen it here - someone posted a code for Hero's Hour if I remember corectly and I redeemed it and I got the message it was successful but someone else who did this before me got the game(he confirmed it).

gogtrial34987: What Harako__ said. The heavy load caused by massive redeems of Amazon Prime keys caused GOG to change the system a couple of months ago.

Right now, if the key is valid, it shows the "redeemed" message - with the load of validity-checking probably spread over multiple servers - but internally all redeem attempts go into a single queue, which are then processed sequentially, and only the first redeem attempt for each key will actually be added to the redeemer's account, with the others silently discarded.
(I suspect that before, there were also multiple servers, but they'd then synchronize / bottleneck to that underlying queue to make certain only one key was redeemed, and that caused the massive slowdowns.)

Fonzer: You mean the message that i succesfully redeemed the game and it will appear later since the site is on heavy load.
But i already had one such case with another game where it said that i redeemed it but that wasn't true.
It can happen that multiple people it says they redeemed the game but only one gets it.
Don't know why it doesn't lock out the game when trying the code to redeem it.
Anyway i still haven't gotten the game so i guess somebody else got it unless it appears in my account someday.

Dawnsinger: The one who the key was originally issued to can see who redeemed it. The issue with the nondeclared rejects seems to apply to Prime keys most often if not exclusively, possibly due to additional complexity involving another database / datacenter in addition to GOGs own.