For instance. I have 100 coins in Numista. I import 100 Coins to OpenNumismat. Now I am adding 10 coins to my collection on Numista having a total of 110 coins. If I want to import from Numista to OpenNumismat I get now 210 coins (100+110) with 100 duplicate coins. I Suggest an option when you import to skip the coins that already have on Opennumismat
Thank you
Fernando Truanovsky