A crest cut through into openwork has no back to it, which means it has to be finished on both faces - and that is where most of the extra work in this sofa goes.
On a solid crest, the carver works the front and leaves the back flat, because nobody sees it. On a pierced one, every scroll is visible from behind whenever the sofa stands away from a wall, and a scroll that is rounded on the front and flat on the back looks, from the rear, like a cardboard cut-out.
So each element here is carved on both faces - not identically, because the back is seen at a different angle and in different light, but modelled enough that the scrolls read as solid forms from either side. The undercutting is worked from both directions too, which is what lets the piercings stay open and clean rather than tapering into a hole.
It roughly doubles the carving time on the crest. It is also the only honest way to make a piece that will be seen in the round, and we build it that way whether or not you intend to place it against a wall - because rooms change.