These invitations given out for conventions is purely propaganda aimed at the converted to make them think they are acheiving something in their ministry .
The reallity is NOBODY and I mean nobody ever turns up as a result of these invitations.
The same is true when they have a campaign at the local KH inviting the public to a " Special Talk" nobody ever turns up,
That is my experience in 33 years as an active witness.
Edit to add :I apologise their was one couple that I know who came because of an invitation.One couple in all of the 33years in about six congregations I attended .and they never came back because they thought they were going to get handouts from a "christian group"