As long as the groups are not enforced at the scanner at many stations, then it's just a pointless operation. I fly quite often from PRG where the announcements are correct but the first people already start queueing with the PRE group and are allowed to pass. I saw Group 3 rejected but it appears PRE, Group 1 and 2 are opening alltogether even though not announced together.

Besides people just unable or unwilling to properly read their boarding passes, the whole naming is just not fully clear and distinctive enough. Group 1 and 2 are both called "Priority Boarding" and the announcement also says "First we start with Priority Boarding". Also what is PRE boarding, it's just a weird naming and not too surprising that some unattentive business chap could believe he can join there.

Personally I think it would be much smarter to get rid of PRE. Is that even written on a boarding pass? Just treat them like a virtual group 0. Just send a staff through the crowd and select those families by hand, tell them to go to the front now and wait there. Then they will board before any announcement is made, so it's also easy to send those back that don't look like assistance or children.