Just create one continuous railing.
If you copy and paste segments you will get joins.
The railing is like a polyline, you just keep picking points in 3D.
It is not like the stair - it can cross over itself.
There is also a pet palette option to extend either end, so if you have an existing railing you can extend it rather than placing a new one.
I am sure one of the YouTube movies showing how to model 'famous' stairs, shows a railing being place on a multi-storey set of stairs.
Just click points in the 3D model.
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