Bacteria that eventually makes milk 'go bad' is always in the milk.
The density of this bacteria is simply very low to begin, yet to be so predictable that a date can be stamped on the milk container at the time of packaging as to when it will go 'bad' because the geometric nature of growth.
Humans are less familiar with the process of collective and collaborative change, so it will be more difficult to pin down a 'date' as to when, however there is no doubt as to the "IF."