I've never used EB sticks....BUT with real butter and the 'bad' margarines, it's normal to see some discoloration if you only use part of a stick...
The 'butter' is sensitive to the conditions in your fridge, and any part that it getting any kind of airflow will change color, texture, and flavor. This isn't harmful (unless it's been sitting there since Thanksgiving before last), but most people cut off the discolored parts before using them. And, I've used partially discolored sticks in baking...since it all mixes with the batter anyways.
I seriously wouldn't worry about it.
Even IF you somehow managed to get a rancid bit of EB with little colonies of stuff growing on it, you'd still be fine. Vegan products do not have the tendency to nurture the REALLY BAD things that cause dangerous food poisonings (salmonella, E.Coli, etc.).
You should only be concerned if your opened sticks of butter were being tossed about in the fridge with an open package of raw chicken or something.
Give thanks to Mother Earth for Her greatest gift...
For without it, we would be lost.