It's a reasonable first reaction to the presence of color bars and grayscales to apply them mechanically and call the result original. But looks can be deceiving: in digital restoration it's always important to think about which sort of data is useful and which isn't.
The key thing to bear in mind is that the color bars represent data at the time the photograph was taken. They do not yield data on how this poster looked when it was new.
This World War I poster was created in 1916. The earliest color Kodak film was produced in the 1930s. Color film rephotography remained in use until digital technology replaced it. So any World War I poster that got preserved by this technique would have undergone at least two decades of decomposition before the photograph was made.
An unknown amount of distortion occurred prior to photo reproduction: if you've ever spent a summer on the Eastern Seaboard, consider the damage that twenty humid summers could inflict. Especially without air conditioning.
But twenty years is the bare minimum here: the date of this particular reproduction was not recorded. The bars and grayscale might be somewhat useful if we knew what year this was taken: 1946? 1966? 1986? That time frame is too large to be useful, which is why I crop out these bars and ignore them. That may sound radical, but yes I ignore them.
The reason becomes obvious when working with this material: substantial decomposition had already taken place. The lower half of the poster is more deficient in blue than the top half, with additional localized problems such as the pronounced vertical yellow band at far left. Chromolithography from this era can behave that way as it ages. The edges had dried and darkened more than the center, which required radial gradient masking to correct, and the brittle poster did not lie flat for reproduction: it needed a perspective crop, then half of the caption had to be rotated separately in order to recreate the original alignment, and then separate corrections had to be applied for the effects of uneven lighting.
So it wasn't until today when another editor at Wikipedia's featured picture candidates insisted that the gray scale bar gives definitive data on how this image looked when it was new, that I located a more specific demonstration of why it does not. First, here's the gray scale bar.
Do you notice something odd about that gray scale and color bar? Let's look in closer.
Copyright Eastman Kodak Company, 1977. That's right: this poster was at minimum 61 years old when the photographic copy was made.