One of the two bills of sale that have survived from Clissett's workshop details two types of armchair. The "Ordinary size, Low back, Rush-seat Chairs, without Arms" is almost certainly the small three-rung side chair, No 6 on the Ladderbacks page. The others are "High back, Ash Rush-seat Chairs without Arms, second size". Until now, I had no idea what was meant by "second size". Now, it seems entirely possible that this new chair is the second size, while the full size side chair is likely to be the first size.
Another little mystery potentially solved.