That is correct. she started here live as Koning der Nederlanden, when rebuild into a floating battery she would have been named Neptunes. Though like you said it could be she was named earlier Neptunes but I've call here Koning Der Nederlanden because I drew here to that standaard, and drew here as floating battery Neptunes. I just added 1820 you give now confusions to the others. I just ment when she was build, not at that time !
I don't know if your Dutch, I can write it by PM in Dutch, I'm not able correct what I want in English!
I am indeed Dutch.
The problem I mean is that the date 1821 is not correct with the name. In 1821 she was called "Neptunus". For me the date 1821 with the name 'Koning der Nederlanden' was confusing
The name 'Koning der Nederlanden' the ship received in 1844. Then in 1859 the ship again was names 'Neptunus'
The confusion comes beceause there round that period also other ships received the name 'Koning der Nederlanden'. So before 1844 there was a complete different ship, a one deck gun frigate build in 1837, named 'Koning der Nederlanden'. and in 1877 a 'ramtorenschip' named 'Koning der Nederlanden' was in service until 1942.