For a moment forget e-tickets. For many years airlines have been practicing "flight firming". Basically this means that every reservation must have a ticket number attached. If, by a certain date, the reservation has no ticket number a message should be sent to the booking originator saying "ticket by date ddmmm or we'll cancel". If the ticket doesn't appear cancellation follows. It's not new and it's nothing to do with e-tickets.
Groups are an interesting issue. One might assume that if you are travelling with a group all of the flights will be in one booking. While this can be the case it's not always true. For instance I know of one major UK operator who has group bookings for journies via a European hub. The group from the hub to destination and back are on one booking. However, because the passengers come from all of the UK to that hub those bookings are made separately. Despite that, one ticket is issue UK/hub/destination/hub/UK. Then you have the operators who sell holidays of varying durations - some people go for 2 weeks, some for 3, etc. What happens then is that there are lots of one way bookings - for example 30 pax every Thursday AAA-BBB and a separate set of one way bookings every Thursday BBB-AAA. The agent simply allocate passengers to the flights that suit the duration. However each passenger has a ticket AAA-BBB-AAA. There are other scenarios but you get the picture.
Now, when the ticket is issued all of the reservations have to be updated with ticket numbers. The flight firming process should catch the problem, but nothing is perfect.........