The files weren't, meant to be super secure, they were primarily meant to be densely filled with saved info and be shorter.
Javascript isn't type-safe, (meaning numbers and strings are somewhat interchangeable) so years have a type change isn't a big deal.
I'll work on better Currency displays for higher values for the next patch.
Popularity is based on an inverse formula (not sure if that's the right term). But it looks something like:
timeBetweenCustomers = 1000-populatarty
So very high numbers may be an issue. I'll rework this down the line.
Personally, I think purposely corrupted saved files are less of an issue & kinda fun to abuse in other games, so this is probably gonna be left in the code unless I get extra time.