We have this early chair
It has 4 fasteners.
Each cushion is attached to the frame at two points. On the early chairs there is one exposed fastener and a second one which is just a metal dowel that keeps the cushion in place but does not have the tension a fastener would. At some point they switched it to two fasteners per cushion that go through the frame and are exposed.
It's a little trickier to get the cushions in place with the insert, then attach the two side bolts without things shifting. I can see why Charles and Ray might have wanted fewer exposed fasteners (more elegant) and why the change was likely made (ease of assembly).
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