I would think in such a situation that the one to be cut would be the no shows, as they are the actual problem. Have you ever had to dismiss those who routinely fail to show or provide a substitute?
I hope your parish appreciates your service.
Yes, there is a policy. Altar servers who go a year without ever no-showing are given recognition for it, but one no-show a year is considered a human mistake and no particular problem. It happens. Depending on the reason for the no-shows, though, eventually the server family is given notice after the third time within 12 months. Some have been given an early retirement, yes. This was a parish that not uncommonly had a waiting list for altar serving: that is, they were usually about right but sometimes were four or five short or had four or five who wanted to serve and they didn’t have room yet. The policy was the same, regardless, but I’d say that in reality the probabation was probably more strict when there was a waiting list, because there was a certain amount of judgment involved in whether to encourage the family to keep trying or to encourage them to admit that maybe altar serving wasn’t for them. (It’s always better if volunteers bow out of their own accord rather than to dismiss them when things aren’t working out. Even after they’re out of altar serving, after all, they’re still fellow parishioners.)
If you know the servers, sometimes you can tell even without no-shows that it is time to move on, because they’re getting so many substitutes or need to consistently ask for so many accomodations in the schedule because they have other demands on their time. (That isn’t to say they quit going to Mass, but that knowing a long time in advance that they can commit to a particular Mass time at a particular church starts to become too challenging.) That’s a bit of a delicate matter, but sometimes it helps to ask if it is getting too difficult to juggle things and letting them know that this does happen to devout families, too.
To return to the OP’s question, it goes both ways! Sometimes, it is the altar serving family that has to speak up and say, “We like serving, it is a privelege and a blessing, but we think it best to set a limit that is somewhat lower than the above-and-beyond level that we’ve been getting.” It is easy for the schedulers to go, “oh, so-and-so will be happy to serve both Holy Thursday and Easter Vigil, we know the family will be there both nights and they’re so good, let’s ask them…” Even if that was true in seventh grade, that doesn’t mean it is true for the 9th grader. Scheduling volunteers is a give-and-take and it takes on-going communication, especially when youth are involved. If the scheduler and the volunteer both appreciate each other, it usually works out just fine.