Loft Skipping Curve

Evening,

I am at my wits end trying to figure this out. Any help would be much appreciated.

I have a curve generated in GH and I'm trying to create a closed loft based on this curve and a height parameter. To do this I'm finding the centre point of the curve, moving it both up and down (although not perfectly in the Z axis) creating curves between 2 points on the original curve and these extension points giving me 4 curves. This much works well but I can't work out how to loft the 4 curves together in to a closed surface. Whenever I try the loft command it simply skips one of the curves.

I have played with grafting/flattening the curves but realised that I'd tried everything logical and had spent the last few hours trying things at random in some sort of vain hope.

Could anyone help with this?

Thanks

Seb