The two DTSs are not equivalent.

DTS1 starts at dts1215a.xsd
DTS2 starts at dts1215b.xsd

The diff paths are

[EvRelationshipFrom] Item: ConceptA with Item: ConceptA
  [EvNext] On DTS1 next was empty, on DTS2 next is A->D

[EvRelationshipFrom] Item: ConceptA with Item: ConceptA
  [EvNew] Relationship ...parent-child, on DTS2 there is a new R. A->D

[EvRelationshipTo] Item: ConceptC with Item: ConceptC
  [EvNext] Relationship ...parent-child, on DTS2 there is a new R after A->C

[EvRelationshipTo] Item: ConceptD with Item: ConceptD
  [EvNew] on DTS2 new R is A->D


DTS1 starts at dts1215c.xsd
DTS2 starts at dts1215d.xsd

All presentation arcs have the same value (1) in the order attribute. All belongs to the same relationships set so no EvNext or EvPrevious must be generated.

The diff paths are:

[EvRelationshipFrom] Param[1]:Item: ConceptA Param[2]:Item: ConceptA
  [EvNew] Param[1]:null Param[2]:Relationship: (ConceptA) to (ConceptD)

[EvRelationshipTo] Param[1]:Item: ConceptD Param[2]:Item: ConceptD
  [EvNew] Param[1]:null Param[2]:Relationship: (ConceptA) to (ConceptD)