Complex sentence: Besides different designs, there were changes involving the watermark and eventually doing away with watermarked paper, changes in currency were also reflected on the stamps: decimalisation in 1971, and Euro changeover in 2002.
Split into simpler sentences: Besides different designs, changes involved changing the watermark and eventually doing away with watermarked paper. Stamps also reflected changes in currency: decimalisation in 1971, and Euro changeover in 2002.