Last fall I posted an experience we had on our flights to Portugal. We discovered during the first flight (the flight attendant alerted us to this) that our tickets did not reflect our Skymiles numbers. I was able to update Delta's computers using the app so we did get all our mileage accounted for.
This year we have flights for next month with Delta and KLM. For months our reservations had our Flying Blue numbers (KLM and AF system) and neither the Delta website or the app would allow me to correct it to show Skymiles. I was on the phone with Tauck air on a different issue and the agent couldn't figure it out why this was occurring as they have our Skymiles numbers. She finally deleted the Flying Blue info and updated the reservations. I checked it out on Delta's website and even printed out the reservation showing them.
Today I was looking at it and my husband and my Skymiles numbers were missing but our travel companions info was in the system though I could only see the last 4 digits of theirs. I updated and saved our info but the system deleted our companions numbers. I suspect if our friends reenter their info ours might disappear again.
Bottom line, stay on top of this. When we check in for our flights I'll be confirming with the agent that all the numbers are there.