Series 1.5 Seat Assembly

I got my newly upholstered seats back from BAS. The upholstery looks nice but I’m confused about reassembling the seat back, bottom, and hinge assembly. The seat bottom has two holes each side that line up with the hinge assembly holes but the back doesn’t have any indication of where the attach holes are - if they are even there. The photos show a standard seat assembly (copied off the Forum) and the sides of one up my reupholstered seats. Any advice on where to go from here?
Art Cutler

You will have to feel through the leather for the holes…possibly with a sharp tool/bradwel

Looks like this under the upholstery: