What part is not in writing? Their are very specific written terms in the bridge agreement that specifically state how it will be enforced such as: f. Measurement of compliance with Hiring commitment and h. Exhaustion of hiring commitment.
First Officers are not eligible for the program until they upgrade to captain and serve a one year lock. The agreement states that the program will run until the most junior pilot on the seniority list is offered an opportunity to participate in the streamlined selection process. They also can wait another year after a failed attempt to take another crack at it.
The point is that it will take years before every pilot on the list upgrades, fulfills the seat lock, and thus has the opportunity to participate in the process. The end result is that every December 31 that goes by means seats in Delta classes numbering from 144-240 annually.