FReferenceSkeleton vs USkeleton

Hello,
I’m loading a skeletal mesh from a new file format (unsupported by UE4 plugins). I have multiple meshes with the same skeleton, but different bind poses.
For now I’m creating a single USkeleton, shared between multiple meshes (body parts). For what I understand each mesh has a Skeleton and RefSkeleton members. Am I supposed to put in USkeleton the Bind posed matrices, and in FReferenceSkeleton the bone transform matrices?
I tried to understand this part from the FBX loader, but I don’t get it.