Crimson Longinus
Legend
My current campaign has been going on a bit over three years now, and it was a new group by the definition of the OP in a sense that it had one new person I with whom had not gamed before. Though they had gamed with one other person in the group. Other people in the group I've known for decades, and we've gamed a lot together.
Games I participate do not always have the exact same people, but there basically is this pool of gamers who all are friends or at least know each other from which groups are formed. This is the case with the Blades in the Dark I'm playing in as well. We've never played with this specific compositions of people, but I've played with all of the people in some other games at some point and most of them have gamed with each other.
So a situation where there is some completely new participant who has not played with anyone in the group before is exceedingly rare.
Games I participate do not always have the exact same people, but there basically is this pool of gamers who all are friends or at least know each other from which groups are formed. This is the case with the Blades in the Dark I'm playing in as well. We've never played with this specific compositions of people, but I've played with all of the people in some other games at some point and most of them have gamed with each other.
So a situation where there is some completely new participant who has not played with anyone in the group before is exceedingly rare.