You can make various styles that would have the back edges displayed. They can't have any of the raster-based edges. As long as you are okay with the basic edge settings, back edges can be used in styles that have watermarks.
I have found that if you have back edges checked on, the setting will be lost if you switch the display styles to transparent. Toggling off the transparency will not reinstate the back edges. To get them again you need to turn them back on in the style's edge settings (or apply a style that has the setting on). I'm guessing this could be a bug. I'll report it to Google.