I saw this interesting story about Indian silver rupees that were recovered from a World War II shipwreck. I'm sure they wouldn't have been in collectible condition, but they were all melted down anyway. But it's interesting, and also to think that this is what happened to a lot of the Indian silver coinage. It seems to be coins from all different dates, not just one year. http://www.cnn.com/2015/04/15/europe/world-war-ii-shipwreck-silver-recovered/index.html
There looking for the 1800 Holland shipping wrecks are the Bu barrels 5c dollar and rupee . There a few out in Indian ocean they claim there one found a 1 - 5 years 1 ship found.
I'd bet these coins were bought for scrap value and cutting them in half would detect plated fakes. I guess English treasure trove laws apply only to the little guys and not the government.