I can answer this is general, but not specifically for Newark.
First, schools know that many accepted families will have options at schools they like better and will not enroll. Having done this for years, they have a good sense of how many accepted applicants will enroll. If it’s 25%, that means that to fill those 100 seats, they need to admit 400 students out of their pool of 700 to yield 100. If they have miscalculated and get only 75, they will need to have – and use – the WL for the last 25.
Likewise, not everyone offered a spot on the WL will take it. There will be kids who are offered WL spots who were accepted at schools they like better and who will decline the spot. Practically, what this means for the school is that they need to offer quite a few WL spots to have a working list that will allow them to use the WL well.
We don’t know how many students NA accepted nor how many WL offers were made unless they tell you. All you know at this point is that they will have a class of 100 and they received 700 applications.
Each school’s working WL needs to address the needs that may arise. For example, in the case above, where they needed 25 more students, they may need 25 boys to maintain gender balance. This means that the WL needs to be built for that eventuality as well as needing only girls. There may be students they love but who can attend only if financial aid becomes available as accepted students decline offers. These considerations vary by school depending on its own objectives and priorities. What this means, in a nutshell, is you can’t really know where you are on the WL.
What you can tell the school, if it’s true, is that you will 100% enroll if offered a spot. When they start taking kids from the WL, their goal is to complete the class, not to continue the uncertainty about who will enroll, so this can help.
You can reach out (a few days after decisions were reached when there’s less activity in the admissions office) to find out about timing as well.
One more thing… some schools use an extended WL all the way through the summer. Perhaps a family moves, a kid gets sick, or an enrolled student gets a late offer from a school they prefer. This creates an opening, and it will be filled from the WL.