It seems I may have inadvertently walked into a little bit of a controversy with that post on Herbemont. Dr Jerry Rodrigues of the University of Cape Town hopes for a resolution in a comment on the post:
Let’s hope that sooner rather than later, researchers in the Department of Viticulture and Enology or at the National Clonal Germplasm Repository (University of California, Davis) or the Plant Genetic Resources Unit (PGRU) at Geneva, New York will not be afraid to make public the microsatellite DNA markers for the true Herbemont.
Whereas Erika Maul from the Julius Kühn-Institut, which maintains the Vitis International Variety Catalogue (VIVC), has this to say in an email:
Herbemont and Jacquez are maintained in European collections and seem not to be endangered. These photos from VIVC could assist to confirm identification.