Thanks a lot for your enlightening clarifications! I suggest to include 
them (or something similar) to the next version of the guidelines.

> displayForm
My reading and interpretation of the semantics of displayForm was focusing 
on "what was to be displayed", which is the reason why I considered it 
quite similar to the planned content of the etal element. I was assuming 
that the connection between "placement of name parts" and "displayForm" 
was relying on the presence of one or more namePart element(s) and thus 
was not intrinsic to the concept of "displayForm".

Your useful clarifications shed light on the semantic width of the 
displayForm element and its difference from the intended contents of the 
etal element.

Thanks for that!