Here is the rundown of differences:
Tires 200=25" 200s=22"
Wheels 200=9" 200S=8"
Plastics 200=2 piece with trunk 200s=1 piece with trunk
200 had a larger front fender and a larger headlight
frames are different
airboxes are different.
Seats are different - all 200 models had steel seat pans - all 200S had plastic seat pans
Gas tanks are same - just different decals (Some early ATC200 models had a different tank due to the gas gap - but they are all shaped the same and are all interchangeable.
Motors are interchangeable although 1985 and 1986 200S shift up and 84 S and all ATC200 models shift down
different gearing
Different tail lights
(Note* 1983 ATC200 was the only ATC200 with front suspension - the front forks are interchangeable with the 200S and 185S, all prior year ATC200 had solid front forks)
(Note* the ATC200s is much closer related to the 1983 ATC185S than it is to the ATC200)
RIP - Yamahondaman!! You will never be forgotten!
RIP - Sam Brehm!! Gone but NEVER forgotten!
RIP - Sandpuppi101 - You will live on in my mind - I miss you friend!