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alas, am not one of the forum's MICMO experts

it certainly appears early seventies

one demarcation is the seat stay treatment at the seat lug

some received the "willow leaf" while others received the simple cutting out of a wedge and crimping as seen on your example

also some received "fish mouth" treatment to the stay ends where they join the dropouts while others exhibit "domed" ends

verktyg has given very specific dates for these differences in his posts

do not have them in me noggin


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