Tangent? Hey that's what this forum is for so feel free to get carried away as much as you want.
Interesting idea of doing a digital copy of missing parts and apply them to the original. Seems easier than trying to airbrush in the details even if you have to go through painstaking efforts to match up to the old photo.
You made a good point about archived material being lost through changes in technology and disaster of course and each time we copy we loose a little bit more of the original. I am even considering copying all my vhs home movies to DVD when available because I know they won't last forever but I will also loose quality when I do. Those and my photos are the first things I try to protect during hurricane season. What a loss that would be.
DJ