I appreciate the responses everyone. Thank you very much.
I didn't want to bias anyone's guesses, so I withheld my suspicions about the I.D. of the chick in question, but EE is the most likely candidate. I had ordered 11 chicks knowing they were going to throw in the extra free chick to make 12. 13 showed up to the post office. I could fairly easily identify 11 of them. The process of elimination left me with the one EE I ordered out of the two remaining unidentified chickies. They looked similar, with the eyeliner and chipmunk stripes, but they weren't exact matches. I lost (read: died) the other one last week so she's not available for photo ops.
Also couple of weeks before the shipment I had inquired about swapping out a GL Wyandotte for one of my Barred Rocks I ordered. They said "No problem, let us know". So I let them know and never heard from them again. So there was always that possibility they'd just thrown that in there too. However, I ended up with all three BR's that I had originally ordered so I assumed they probably didn't do the swap.