The first close up of the Indian Head nickel shows the year being 1937. When Johnny puts it on Alex's casket, the year is 1938.
In all other shots of Washington D.C. being destroyed, we see the shock wave hit the Capitol building from the south. In this episode, the shock wave hits the Lincoln memorial from the east. The Lincoln memorial is due west of the Capitol, so there is no ground zero that can result in a shock wave hitting these two points from these two direction.