it would seem if you are "eligible for pre board", you should not even consider printing out your boarding pass earlier, since once you get to the airport it does not matter what "boarding group" you are in A B or C, you as a "pre board" are actually in a "different" class and board before any of the other groups
in addition to gail's "special needs" grouping, there are also those with "special needs" of "working" the system so they get on "first" even though there is nothing requiring the pre board process for them ( have seen this more and more lately )
in addition to gail's "special needs" grouping, there are also those with "special needs" of "working" the system so they get on "first" even though there is nothing requiring the pre board process for them ( have seen this more and more lately )