Interesting wording regarding Mileage Plan partner Delta at Alaskaair.com's site:

To qualify for mileage accrual, flights must fall within the eligible flight number range. To ensure flight credit, the two letter airline code (DL) must precede the flight number (for example, CX XXXX) on your ticket receipt or boarding pass.

I recently flew a roundtrip to Jacksonville from Los Angeles. The ticket was purchased on the Alaska website routing LAX-SEA-ATL-JAX. The flight segments flown on Delta metal (SEA-ATL-JAX) show up as AS XXXX codeshares, not DL XXXX as indicated above.

I notice that my Alaska flights have posted, but no Delta flights have. Normally, Delta is one of the quicker partner airlines to post (much quicker than AA) and last year similar AS purchased tickets involving AS codeshared flights on Delta metal were credited.

While it seems unlikely, I can't help but wonder if things have changed, especially given the wording about DL mileage accrual above. If they have and mileage may no longer be earned on AS codeshares involving DL metal, I'll definitely avoid buying tickets where AS/DL combine.