You could simply submit a online contact form on Longines official website, sign up for an account and follow the instruction here --
https://www.longines.com/certificate-of-authenticity
They will get back to you with the extract information in email, and also mail a signed extract of archive to your address. I had some problem with the contact form, but I contacted them on facebook, and they gave me an email address for me to email their heritage department directly. Mine took 10 days to arrive in my mailbox.
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