Hi Nick, and welcome.
As someone who lives next to the eastern End of the Solent and has a medium sized vessel at Chichester Marina, and goes up the Solent quite often, yes Spitsand Fort is incorrectly shown on the map, although the actual Fort is in the correct loation, I think.
I think Nomansland and Horsesand Forts are in the correct locations, though.
What makes you say that they aren't? They did get moved in one of the updates to the game, so perhaps you haven't got the latst version installed?
What co-ordinates are the three forts in your game? If you let me now, I'll check it out for you.
Thanks.