the production company, AIC, made extra 
xerographic copies of the sketches, had them 
painted, kept them for a while, and then released 
them to the public.  So they're essentially 
official reproductions of a wide variety of 
cels.  Unfortunately, it appears that no one in 
the company has a record of which cels had repros 
made from their sketches.  Thus, the importance 
of checking them against the original material 
(video) before you buy, especially from a source 
such as ebay where sellers may not have 
adequately checked the authenticity (or may not 
be as honest as we'd hope).