Since update from PackEdge 10.1.1 to PackEdge 12.1.2, the margins are not visible any more in Extended Preview.
By default the margins are only visible in Contours Mode. To make the margins visible in Extended Preview, one needs to add (any kind of) Spot Color and define it as Technical in the Ink Menu. This "trick" does not work any more since update from PackEdge 10.1.1 to PackEdge 12.1.2.
This was solved in PackEdge 14 (ALPHA) build 14052.