Thanks for the answers.
What I guess I didn't realize was that Delta has the power to grant precheck on a flight by flight basis. Since I was batting 100%, I sort of assumed that Delta had done something to register me with the TSA, which then granted me a known traveler number, which I never received to share with other airlines, and possibly "owned" this.
The consensus seems to be that Delta never "got me into the program" but instead had the power to give me precheck based on my history on a flight by flight basis.