I think it does still happen.
Pretty sure there’s wording that you can’t use credits for anyone not on the dining plan. Not that they necessarily enforce it strictly, but if you have 4 in your room I don’t think they allow you to pay for 6.
That isn't what happened.
We had a group of more than 5 people with everyone was on the DDP, but we were 4 people in one hotel room and everyone else was in the 2nd hotel room, with one child (age 3-9) in the group.
Room A : 3 adults, 1 child
Room B: 4 adults
I distinctly remember in Tutto Italia we ordered the way we were supposed to order, and gave the waitperson our two bands, but the meals were not charged to the correct rooms. The child meal was 'charged' as an adult meal, to the room that was all adults.
Meal charged as:
Room A: 3 adult meals
Room B: 5 adult meals
In that case, the CM did indeed too many meals to the adult-only room. A second CM made a similar mistake. I think that was at 'Ohana.
The Tutto one stands out all this time later, because it took SO long to get the bill settled, that we missed the fireworks. It was so slow, that we figured it would be much faster to talk to the hotel concierge.
All of this is part of why we stopped getting the DDP. With a bigger group, table service meals were very slow. We often had to wait well past our ADR time just to get seated, and then it took another half hour or more (requesting check to final payment) at the end of the meal to get the check settled, even though we always left the tip in cash.
Hopefully the current DDP is better, and it sounds like the OP's group is all in one room.