I never saw Yu Gi Oh but read an interview of 
Shingo Araki (to me the best character designer 
ever: Versailles no Bara, Saint Seiya, Captain 
Harlock), who worked on it. He said that the 
first season of the series, made by the Toei 
animation did not have a good audience, so the TV 
channel decided to stop the series. But the 
success finally arrived with the diffusion of the 
very last episode of the first season. So the TV 
channel finally decided to go on with a second 
season, but they asked another studio to do it, 
because they were not satisfied with the work of 
the Toei. Only Araki Shingo went on working on it 
because he didn't work for Toei but was an 
independant (Studio Araki Pro). Now, because of a 
problem of rights, no one is allowed to show this 
first season anymore. In many countries (probably 
all but Japan) Yu Gi Oh started with season two.

So I guess that cels are only from season one 
(made by the Toei), and the next seasons were not 
made with cels...

Olivier