So this is one off and I could not find a thread that was similar.
It makes sense to me why the tank needs to be Oxygen Clean - you will be filling directly from the O2 to the Scuba Tank - slowly and cleanly.
What I don't understand is why the compressor or fill station if it is pumping Grade E air after the O2 has been transferred but is not O2 Clean is required... Is there a resource or a simple explanation for why the fill system to be O2 Clean?
Grade E is a s*** standard to go by. I can produce Grade E from my bicycle pump. Something like the Canadian CSAZ275 will give you a better idea of whether or not the air is OK. However you would need to see a recent air report to see whether or not the compressor is capable of producing OCA air (which is a made up standard by the scuba agencies BTW).