A friend of mine used to collect Disney cels and 
at one time said cels prior to 1965 were hand-
inked, with 101 Dalmatians being the first 
animated film completely lined with the xerox 
method. 

It seems Disney has been poking at xerox line 
method since the 50s so I wouldn't be surprised 
if Japanese cels were done the same way. 
Supposedly, the lines were xeroxed, but 
were "enhanced" with some hand-inked lines. 
(which may explain why some art galleries 
say "with 10 hand-inked lines" as a description 
of some cels.)

I'm sure the line method varies from series to 
series, studio to studio, though. 

It's been a while though so my mind may have 
melted a few things together. ^_~