Sorry if my question "what are you going to do with the data" sounded like "what use is it?" I didn't mean that at all. I think it's a great idea. In fact I did something similar myself years ago, but by hand, with 70+ physical yearbooks and an excel spreadsheet. For me one of the most interesting things I found was the dramatic differences from country to country surrounding 1975. For some countries such as the Phillipines the impact was dramatic and for other countries such as Italy there was no impact whatever.
Sounds like a good idea. I wish I knew how to do it.
Alaska and Hawaii in or out US, South Sudan, Rhodesia, Zambia, mixing changing names all over the place. Complicated stuff. Good luck.
What are you going to do with all the data?