Grandpa Gene is rummaging through his WWI memorabilia and tells Bobby how he shot a German soldier in the head and kept his helmet as a souvenir. However, the helmet is the old style Prussian helmet (Pickelhaube) with the spike on top. These helmets were quickly found to be ineffective and by the time the US entered the war, these helmets had been replaced with steel helmets, so it's not something the German soldier would have been wearing.
The ad for "free kittens" on the bulletin board when Peggy posts her roommate notice shows the phone number to call about the kittens is (212) KL5-0138. However, there is no need to show the area code since New York City only had 212 until 1984. Unless there are callers from out of state (or from Upstate New York), the area code wouldn't be needed as 212 would be the implied default.