I just came into posession of the attached 5 
layer cel, and I'm curious about the layer 
numbering.  The bottom three layers each 
represent one of the characters, have the usual 
cel number in the format of Letter/Number, and 
all three also have what I believe is called a 
sequence number (667-668B, then what looks like 
the letter "Z").  It's the top two layers that 
have me perplexed.  The top most layer has 
nothing on it but the cel number; F1, written in 
orange and with the 1 circled. (A key cel of 
nothing?), and the second layer has no cel 
number, but does have Washuu's blue halo. Neither 
of the top two layers have the sequence number.

Any idea what's going on with these top two 
layers?