There's really two questions I'm asking.
Firstly, when maps are produced of stars and galaxies, are they just produced as we see them now from our viewpoint? Or are they based on the motion of those bodies? Eg Galaxy X is 1 million light years away and we know it's moving at Y speed, so it's real position now is actually 1 million years worth of movement along that trajectory.
Secondly, are those things taken into account when doing other studies of things like dark matter? Ie things are actually further apart than what we see because we're seeing them as they were Z million years ago. I would expect that would affect calculations for things like how much 'missing' matter there was.
To try to further clarify this second question, simplifying things to 3 points on a triangle... if we're at A and we observe points B and C which are X billion light years apart, then the effect of gravity on the speed of B and C moving apart would have been greater in the past when they were closer together and furthermore the effects of the current gravitational force will take more than X billion years to reach the other object. As far as I understand, dark matter is a way to account for observed gravitational effects that can't be accounted for in other ways. When astronomers do these calculations, can I assume that they have taken into account the time delay in the effects of gravity between galaxies? Or have I in my naivety, stumbled on some profound insight! (I doubt it.)