Hi Collecto,
You are right a bank cel is a cel that get used 
more then once, for instance a henshin cel, and 
an attack cel are usually bank cels along with op 
and ending cels . These cels get used once for 
the sq then they reuse the seq over and over 
again. I'm not sure about the ebay auction you 
have posted, ytou would have to check Sailor 
stars episode 199-200 for that cel to determine 
if it is a bank cel.good luck
starfighter319