In a perfect world, everything should follow their own orders.

However, it is not always the case.

For UA, GAs tend to stick to the list if they can. For CO, it is hit or miss.

But sticking to the list or not take a lot of consideration, such as:

1. Your final destination and routes. For instance, for LHR-EWR, if a passenger is travel on LHR-EWR-IAH and another one is LHR-EWR-CLE, the one going to IAH will tend to get the VDB (as that person can re-route on LHR-IAH non-stop, but not the one to CLE).

Also connecting to an international flight is certain a no for VDB (as you may miss your flight).

2. How many people are traveling with you

1 is the best. Once I have a 1K couple who were before me on the VDB list. But still I was the first one got it.

3. Checked Baggage

A lot of people claim that it matter. The reality is no - remember unless it is an international flight, the GA does not need to offload your baggage at all, assuming you still want to make the trip same day.

(I have once VDBed by CO with 2 checked baggage. The GA did not offload my baggage at all, as my replacement flight leaves about 45 minutes. What best is CO even transfer my baggage, upon arrival, to UA Baggage Desk and they were safeguarded by UA personnel.)

4. Cabin Class

GAs tend not to choose premium classes passengers. Once, I had to push for it.

But in general, as soon as you are a Premier Gold or above, VDB should not be difficult to score.