Chippendale chairs (18th C.) almost always have glue blocks.
(I say almost because there are always exceptions to the rules.)
Not the modern type that were screwed on, but a small piece
rubbed on (with glue) between the front rail and the leg,
made flush with the back surface of the leg, and another
piece rubbed on the side rail over the leg and glue block.
Later on, on transitional chairs (late 18th and early 19th C.),
I have seen corner reinforcements that were pieces of wood
let into ramps cut into the rails. While they don't reinforce
the leg joint, they triangulate the seat to keep it from racking.
Early French chairs often did not have corner blocks.
Next Chippy I get in I'll take pics to illustrate with real examples.
Until then my amateurish illustrations will have to suffice.
John Coffey
Locust Valley, NY