We often use only a few slices of bacon, seal the remainder, and use it for at least a month (don't use bacon all that often).
Can't imagine most bacons not containing nitrite/nitrates. Don't have any bacon in the fridge but looked at packages of franks, chorizo, kielbasa and Genoa and they all listed nitrites and or nitrates.
Why the color change I don't know but if it smells OK I'll bet it just fine.
Before criticizing a person, walk a mile in his shoes - then you are a mile away and you have his shoes!