I just picked up these two chairs with Thayer Coggin labels, as well as a store tag dating them to 1974. I can't find an exact match anywhere. Given the date and TC tag, can I say they are Milo Baughman? Would anyone else have been designing chairs for Thayer Coggin at that time that so closely resemble Milo Baughman designs? 
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I think you can safely say they were designed by Milo Baughman, he had an exclusive contract with Thayer Coggin. The only other designer at Thayer Coggin was Allan David Gould, back in the mid to late '50s. He did the "compass chair" and some other cool things.
You might try TC's customer service, I think they're even buying back some vintage pieces now too.
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