There's a thread in the Marriott forum about info they collect on you and people requesting copies of this which results in basically a complete data dump:

Be Aware, All Marriotts Have an Internal System Where they can criticize you!!

Don't know if DL will do the same thing especially in jurisdictions that don't mandate it, but the instructions in the Marriott thread link you to their privacy page, so analogously in the DL case I might start with item 9 under DL's privacy policy.

https://www.delta.com/us/en/legal/privacy-and-security

Wonder if I could use this to fill in gaps in my flight log too though my missing info is mostly on other airlines from back in my kettle days.