.. never been clear on the meaning of loppon.
Maybe some of my old notes (although they are rather random) could add to your study of the word "Loppon", basically I think when they refer to just "Lopon" this means teacher, especially a scholarly teacher, whereas a "Dorje Lopon" has the connotation of being a "Vajra Master".
"Lopön is a Tibetan word that means 'teacher' (acarya in Sanskrit)"... according to The Lotus Garden site, also
Mindrolling Jetsün Khandro Rinpoche appointed western Lopön's at Mindroling Lotus Garden:http://www.lotusgardens.org/lopons/index.cfm
There is also the term "Dorje Lopon" (Wylie: rdo-rje slob-dpon)http://en.wikipedia.org/wiki/Dorje_Lop%C3%B6n
(A Dorje Lopon) has the meaning of being a "Vajra Master".
Ani Lopon Yeshe Lhamohttp://damchoe.wordpress.com/2007/01/18/female-teachers/
"Lopon" Tenzin Namdak (is of course, also a Rinpoche)
Lopon also spelled Loppön, is used for "Loppön" Jigme Rinpoche
Instance of a non monastic teacher in Drikung Kagyu being titled a "Dorje Lopon" in the West:
Asheville-based Urban Dharma NC founder Hun Y. Lye honored by Tibetan buddhist organization
"Dr. Hun Y. Lye, Founder and President of Urban Dharma NC, has had the title and position of “Dorjé Lopön” (Vajra Master) bestowed upon him by His Holiness Drikung Kyabgön Chetsang Rinpoché, the leader of the Drikung Kagyü lineage of Tibetan Buddhism at Drikung Kagyü Institute in Dehradun, India, on March 10, 2013. This is the first instance the title of Dorjé Lopön has been given to a non-monastic teacher in the Drikung Kagyü in the West."