Take the tinfoil hat off, junior.

All that tells you, is what state with the code of 18. It doesn't tell you where you are specifically, only the plant of which the jug of milk was made in. In this case, it was made in Indiana (not sure if it was based on the number of states in order, which would make it wrong since Indiana isn't the 18th state, more like 19th but whatever).

I do happen to work retail and the plausibility of how the milk ended up the way it did is several. The plant didn't do a good job. Your housing conditions such as temperature and where you stored the milk matters overtime. Someone working dairy didn't care enough to efficiently stock the jug per company standards. Something.

Anything. I've never had a milk jug just come like that though, since I buy almond milk anymore.