A better example might've been something like this:
Code:
In the 1970s...
In the 1970's...
In the first one, you can pretty much tell that you're referring to the era, because the author took the "bad grammar" move and left out the apostrope. The other could be a possessive with "1970" referring to something made in '70 that was revealed in context, or it could be the same as the one above it. You just can't tell without context.