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davidcyclebackAs opposed to from the 1800s, the majority of post 1900 cards, even early ones, were photomechanical reproductions of something. In other words, for a 1910 or 1920 card there was more likely than not a physical photo or sketch or painting it was reproduced from.
For many prints, you can tell if they are handmade (original) by looking closely at the printing. Some ink patterns can only made by hand. For example, you can look closely at some Picassos and determined that the print could only have been made from the orignal printing plate.
The T206 Honus Wagner is a reproduction of a photograph. There was a physical photograph, possibly with added details in ink or whatever. However, the photo probably had none of the bright colors that appear on the card. The colors were likely added somewhere/sometime else.
Old printing plates do wear down. The details would get weaker and often times the artist would go back and add more detail. In an academic catalogs of the prints of famous artists, like Rembrandt, there are details of different 'states' the prints come in. In cases, you can date when the print was made by identifying the state. For some types of prining, like etching, it is known about how many prints can be made before the printing plate has to be 'reworked' (reworked = artist going back with his tools to add detail to the plate).
Of interesting note, in the fine arts, the printing plate is often physically defaced, called 'cancelled', to prevent any more prints being made from it. An example of cancelling would be carving a deep cross across the image on the plate. Commonly, a print or two is made from ruined plate to demonstrate that the plate was destroyed.