You couldn't use litres though, the Americans wouldn't understand it
They would soon learn! In fact the game might be a good educational tool.
Or if Orteil really wanted to go over the top he could have a setting on the Options screen to choose whether to display milk in litres or express it in furlongs or cubits or whatever arcane units they use over there.
I found the milk % display useful because my spreadsheet needs to calculate it and use it, so I often used to check to make sure my calculated % matched what was displayed in the game. If it did not, it told me that there was some achievement I had gained and had forgotten to include in the spreadsheet.
I must say the term (percentage) always bothered me. Percentage of what? If I had written the game, I would have given it in litres. (I nearly said "would have expressed it", but I can't do that because I'm a bloke.)
Surely you must be able to find some feature/upgrade that has gone missing, which would explain the loss? Some people have reported spirits becoming unslotted in the pantheon when they close down and restart the game. I've found that it's possible for a slot to be empty even though it appears to be filled. A couple of times I have seen the Jeremy image in the Jade slot, but if I hovered over it the image did not jump up and down, and the popup said "Slot empty". Mokalsium can easily make a difference of a factor of 2. Check your pantheon. That's the only thing I can think of.
If that fails, surely you must have posted one of your game codes to the site at some stage? It won't contain recent production, but it wouldn't be as bad as losing two years' worth.