It says that the map in the 1880 was based on Father Kim Degeon's Carte de la Corée of 1846. (Is this 金大建's 朝鮮全圖, 1846?) I haven't a slightest idea if Father Kim Degeon and Andre Kim was the same person or not. The map in 1880 looks more accurate - it depicted Ulleungdo as "Oul-neung-to (Is. Dagelet)" and the shape of "Ou-san" looks like today's Jukdo. It seems to me that mapmakers noticed that Ulleungdo was Dagelet island in the period between 1855 and 1880.
Carta de la Coree (1846):