I'm not sure about 200s but on 300s you can see a small circular embossed stamp towards the back of the cylinder head (driver's side) with 2 sets of numbers, one on top of the other. I'm not sure what the top set means (it could be the week number) but the bottom set is the year.
 
Date on cyl head as mentioned is a good guide
Early 200tdi had an extra breather to the rocker cover, deleted from later models
 

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