I try to copy some layers from folder A to folder B. In folder B this layer names exist and so Rhino ignored it. Better would be, if a popup window would say “layer names exist, do you like to merge the layers?”.
Often I get parts from my clients and I build the assembly. In this case it was layer directory “cabin front” and “cabin rear”. Both layer directories contain the same layer structure. So, in this case the automatic merge doesn’t help. (But thank you for the hint. My screenshot was a little bit reduced.)