I was also in doubt reading the document. It also states at page 52: "If the three proposed sections are inscribed on the World Heritage list, the European frontiers of the Roman Empire would be distributed over four separate World Heritage properties. "
On the other hand, the description of the Lower German Limes says: "The nomination of this part of the Limes as an extension of the FRE WHS"
I think I have bottomed this issue!
The Netherlands version on the UNESCO site of the Description of the Lower German Limes ( http://whc.unesco.org/en/tentativelists/6298/
) differs in many respects (way beyond the obvious one of having different proposed locations) from the German one ( http://whc.unesco.org/en/tentativelists/6299
) which you quote above!!! In particular it lacks the statement which mentions the word "extension"!
!! Instead it states "The Lower German Limes will be nominated as a single, distinct (serial) property, following the nomination strategy for the Frontiers of the Roman Empire, written in 2017 by the States Parties involved in the proposed nomination of the frontiers in Europe"
The audit trail for this goes through the "Koblenz Declaration" of 23/6/2004 but achieved "official" UNESCO status in a decision as recently as at the Krakow WHC in 2017 (We missed that!!). This document - https://whc.unesco.org/archive/2017/whc17-41com-8B-Add-en.pdf
addresses the issue of "LARGE COMPLEX SERIAL TRANSNATIONAL NOMINATIONS AND THE NEED FOR NOMINATION STRATEGIES"
(see Page 21) using the FRE as its main example for action but mentioning also a number of other Nominations involving 4 or more States Parties which have been/can be so complex as to benefit from an overall "Nomination Strategy" to be developed across all the elements. For the FRE it proposes one which "augment(s) the current serial property via three serial nominations for the Lower German (i.e. Lower Rhine) frontier, the Danube frontier, and the frontier of the Roman province of Dacia"
This general proposal (framed specifically in terms of the FRE ) was accepted at Krakow as Decision 41 COM 8B.50. See http://whc.unesco.org/en/decisions/6922/
So - at last we arrive at an answer to the question posed by Zoe 2 days ago - in line with the decision reached at Krakow, and in contradiction to our earlier incorrect assertions (!!!), the FRE "Lower German Frontier" should be nominated as a separate WHS rather than as an extension !!!
The further anticipated elements of the FRE in Europe (Danube and Dacia) will ALSO be nominated as separate "clusters" with their own justification, OUV etc etc. As a result Germany would finish up with THREE different WHS covering different areas of the FRE!!!
The existing inscribed elements of Hadrians Wall, Raetian-Upper Rhine and Antonine Wall will remain as a single "WHS" on the argument that these 3 elements, despite their geographic separation, cover those sections of the Frontier represented by "Walled Fortifications" (as opposed, for instance to "River Frontiers" as in the Lower Rhine and Danube) and, as such, fit "logically " together. This strikes me very much as a post hoc rationalisation which avoids having to break up an exisiting WHS!!