ID Daybed Sofa  

More photos

The base either has particle board or some form of plywood underneath veneer. The rest is solid wood.

I don't believe it has any particle board, perhaps veneer over solid wood on seat area.. see pics

Solid wood means solid boards, joined on their sides, and subject to wood movement.
Beyond that there are various more modern engineered products that are design to create a wooden substrate, suitable for veneering, in larger dimensions than trees have the courtesy of growing it for us, and not subject to wood movement. These are things like lumbercore (not something you can really buy anymore), plywood in various forms, particleboard, and MDF/HDF (medium/high density fiberboard).
The substrate of that base has to be an engineered product that is not subject to wood movement because the edge banding is still attached. Might be a nice grade of common plywood, maybe lumbercore even.
Sorry I can't tell you who made it.

Fabulous, I stand corrected. I'm here to learn, thank you for your info.