I believe that additional sound deadner was added to the Cossie doors to give it a better sound as it shuts?
When I bought my car the LH door had been previously replaced due to an accident, when I took both door pads off, there was deadner in the RH but not the LH. I simply fitted a similar self adhesive deadner and they now sound and feel the same.
If you tap an original cossie door it sounds alot better than a 1.3 standard car.
Cheers
Paul