Thanks for the new upload but I only see two materials in the Linked-Seat.3dm so something about the issue you are seeing is not saving with the file. I’ll let you know if I can figure out how to reproduce it here for a bug report.
Unfortunately, I don’t think this will be possible due to how the block system works in Rhino. See @andy’s comment on https://mcneel.myjetbrains.com/youtrack/issue/RH-44215