Paul mentions the keystone size on later GG1s. This brings back my college years. We were in a class known as The History of Architecture. Professor John Clauser was fascinating to listen to. We learned how societies art and architecture evolved as each civilization progressed.
For example, Ancient Greece, the cradle of Democracy started as an idealistic people. Their thinking was clear and their art and architecture expressed this idealistic mindset. As time went on and Greeks became more powerful and affluent, so did their expression in art and architecture become more ornate.
There are three main periods in the Greek civilization. Thus three periods where architecture, for one can be expressed. The Doric or beginning period of Greek culture. Architecture was expressed in it's pure sense. Not ornate but rather strong with idealistic yet simple lines. The middle period known as the Ionic period, when Greece was finding it's plan in the ancient world. Architecture became more ornate, but still expressed purity. Finally the Corinthian period. This era was the final part of the Greek civilization. Greek society became decadent. Art and architecture reflected this. The reason behind the overly ornate architecture was that as a society, Greece was loosing it's power through greed and corruption. The clear thinking that had prevailed was lost. So in order to make themselves appear powerful and respectable, architecture became overly ornate.
Ancient Rome thought very highly of Greece and copied much of their accomplishments in government and art. But Rome fell into the same trap and their architecture reflected the downward spiral of society, just as the Greeks before them.
This brings us to the Pennsylvania Railroad, among others. The docketing of the GG1 is a fine example of Doric, Ionic and Corinthian periods. Originally, the GG1 was adorned with elegant yet understated striping and small keystones. The lettering was simple and straight forward. It can be said that the Ionic period for the railroad was skipped. In the post-war period, about the early sixties, when the railroad was in decline, the decoration of the GG1s became bold and overdone with a wide bright stripe and large keystones. It can be said that this was the railroads way of letting itself be known as it's influence in transportation declined.
We, in this hobby don't really care that the GG1 went through different paint schemes. In fact, we relish being able to have each or as many as we can afford on our model railroads.