Locally I see a good many trains with the 1267 placard. It piques my curiosity to see one train eastbound and one westbound at the same time, both full. Why not leave the oil back there closer to where it came from instead of expending the transportation on it?
Not all oils are equal. Different refineries are optimized for different oil, heavy, sour, light, sweet, etc. That could be one explanation.
You might also be seeing oil moved that is partially refined, gas-oil product for example.
Too many variables to know for sure, what you were seeing.
Rather than replacarding empty unit trains as "Residue" cars, they just leave the 1267 DOT placards on. Look at the springs on the trucks to tell if they are loads... or depending on the ruling grade the power assigned. I can tell just from the sound.
I recently spent a weekend with my old RR buddies out near Horseshoe Curve at a friend's B&B that caters to train nuts (it's a niche market, but very lucrative for the location)... a LOT of loaded CBR unit trains eastbound, an equal number of empties westbound.
I love the smell of interstate commerce in the morning.