They could have added a disclaimer to the ending - "Yes, they could have possibly had an atomic weapon by 1946 but even the German High Command knew that there wasn't going to BE a Nazi Germany by them. The US/UK from the west and the Red Army from the east made any hope of these secret weapons seeing production sheer folly.
It is no secret that before and during WWII, Germany's military was way ahead of the military engineering and design game. So many of their technologies after being captured by the ALLIES found their way into modern warfare and even science today(rocket technology). The design and function of their military machines were so superior to that of the Allies that in some cases comparisons couldn't even be made(German Tiger tanks to the early US Sherman tanks, as an example). However, the sheer numbers of the Allies' forces and the fortunate fact(for the free world) that incharge of all these German technologies was a NUT job, Hitler,helped the Allies prevail. Engageing his forces on 2 fronts, in addition to Africa, plus all of Hitler's own fanatical strategies and decesions(the Final Solution-the extermination of Jews to name one), plus limited resourses, finally caught up with the 3rd Reich and all of the German military.
Could they have bombed NYC? They were working on longer range rockets like the V-2 with multiple stages. (captured after the war and detailed in full by Dr. Von Bruan, later our very own NASA guy!) The A-bomb would have probably followed if we(The U.S.) had not developed it first with a little(captured) German help.
Which begs the question, WHAT ELSE IS LOCKED UP IN THESE SECRET STORAGE FACILITIES?