Ha, I had been looking for the Pinned property under the Stairs Class and completely missed that they were methods for MultistoryStairs Class 
Bit of an odd one here, but it appears if you Unpin > Pin > Unpin using the API, you’ll lose the railings on the in between levels. I’m guessing its because the Railing’s host ID is essentially deleted and recreated when the stairs are repinned. Just something to be aware of.