What M says is probably true. 

I once received a couple of cels from a deputy
that I did not win. One of them was from Slayers
(I had bought several items from the same
show/seller in a short time frame). The other was
from Sailor Moon, which I have not seen and know
nothing about. 

I thought they were both freeebies and had them
for several months. Eventually, the deputy emailed
all their clients asking if anyone had received
unexpected cels. I sent them a scan of both cels.
As it turned out the Slayers cel as a real freebie
and the Sailor Moon cel was someone else's.
Somehow the SM cel had gotten mixed up with my stuff. 

The YJ seller I got the Slayer cels from, sells a
lot of cels from a variety of shows. They probably
put multiple items in the same bag since they were
all going to the same deputy. The deputy then must
have missed the SM cel in the bag and sent it to
me with my Slayers cels.