CREATE TABLE table_31381 ("Value" TEXT, "Dimensions" TEXT, "Main Color" TEXT, "Obverse" TEXT, "Reverse" TEXT, "Watermark" TEXT, "Date of issue" TEXT)

How many different dates of issue are the for the coin with kumsusan memorial palace on the obverse?
SELECT COUNT("Date of issue") FROM table_31381 WHERE "Obverse" = 'Kumsusan Memorial Palace'
SELECT COUNT("Date of issue") FROM "table_31381" WHERE "Obverse" = 'Kumsusan Memorial Palace'