50 öre in copper-nickel was made 1920-21, 1924, 1940 and 1946-47. Minting of silver gradually ceased during WW1 and for the 50 öre it wasn't resumed until 1927. The reason of course being the rising price of silver due to the war. The same happened at the outbreak of WW2 in 1939 (but silver minting was resumed already 1943 for the 50 öre). There was also an increase in the silver price right after the war, which I guess explains the 1946-47 issues.
Similar patterns show for the 25 and 10 öre coins (silver replaced by copper-nickel), and for 5, 2 and 1 öre (bronze replaced by iron).
About 1951, yes it is correct that no Swedish coins with that year exist. Swedish coins have the portrait and/or monogram of the reigning monarch, and as triggersmob already pointed out, we had a new king, Gustaf VI, in 1950. The new coins were not ready until 1952. (Minting actually didn't cease during 1951, it continued but with the date frozen at 1950. Thus the date 1950 is more common than others.)
This was repeated in 1973 when Gustaf VI died and was followed by our current king, Charles XVI. Not until 1976 were the now coins available, so no coins with the years 1974 or 1975 exist, but plenty of 1973s.
Similar patterns show for the 25 and 10 öre coins (silver replaced by copper-nickel), and for 5, 2 and 1 öre (bronze replaced by iron).
About 1951, yes it is correct that no Swedish coins with that year exist. Swedish coins have the portrait and/or monogram of the reigning monarch, and as triggersmob already pointed out, we had a new king, Gustaf VI, in 1950. The new coins were not ready until 1952. (Minting actually didn't cease during 1951, it continued but with the date frozen at 1950. Thus the date 1950 is more common than others.)
This was repeated in 1973 when Gustaf VI died and was followed by our current king, Charles XVI. Not until 1976 were the now coins available, so no coins with the years 1974 or 1975 exist, but plenty of 1973s.





















