Andy,
I suspect you've fallen foul of one of the new fences that's appeared over the last couple of years ( don't think that the OS can keep pace with the Bowland fencing contractors ) and ended up following the incorrect fence. Even some of our home-grown Boweland lads have been known to get there fences wrong, particularly in clag. You can't miss Fiendsdale Head (when you hit it), a great big ladder stile over the ridge fence, surrounded by a huge peat morass with an obvious path coming up from Fiendsdale ( E ) and an equally obvious path coming up from Bleasedale ( W ). A bit puzzled how you dropped W and got back to Dunsop? From up there you need to drop E or SE.
Easy to be wise after the event, but I always check any fenceline that I'm following ( in poor visibility), using map and compass to ensure that it's heading where it's supposed to.
Ian.