In many of the flags often used to illustrate Danish regiments in the period of the NYW 1688-1697 The F4 cypher for King Fredrik is shown.
This is not accurate as the King at the time of the war was Christian V
who had a completely different cypher incorporating the letter C and an arabic 5. He reigned from 1672-1699 I believe.
The mistakes perhaps eminate in the English speaking world from Sapherson's book on the Danish Army which rightly deals with the army in the reign of Fredrik 4 and illustrates the colours for the right period with the right cypher. Retro fitting the flags to the earlier period seems to have created the oversight which I too did with some regiments a few years back.
Thought this was worth pointing out as the Danes are a significant component of William's Army in Ireland and Flanders and popular with gamers.
Being expert on the Danish succession was not mandatory at my school