Le Corbusier date/authentication help LC4  

I recently purchased some Cassina items at an estate. I also purchase an LC1 and this LC4 Chaise Lounge. Presumably made by Cassina. The LC1 is stamped 1005 and signed. The LC4 has no signature. Just stamped 15 twice under the headrest where the joints meet. Belt buckle stamped made in Italy.
I know Cassina started production in 1964 so Im assuming the chair is the 1005'th one made. But the chaise is the pickle. Some input would be appreciated..
Thanks!
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