I sent a fax to Korean air LA office to get missing mileage credit (Delta).
(I have done this more than 5 times. Last time was 8 months ago)
But this time, they wanted the documents maile to them.

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Korean Air wishes to express its sincere appreciation for your valued patronage and for
providing us the opportunity to serve you as our Honored Guest.
In reference to your mileage update request, we are unable to process it at this time due to the following;

A. ADDITIONAL DOCUMENT(S) REQUIRED.
In addition to the documents you have provided, we would like to request the following documents.
(PLEASE RETURN BOTH DOCUMENTS TOGETHER).
O Original Ticket/E Ticket coupon(s)
O Original boarding pass(es)
O Others; ADDRESS TO; KOREAN AIRLINE, SKYPASS SERVICE CENTER
1813 WILSHIRE BLVD., LOS ANGELES, CA 90057