You transfer from one flight number to another. I think that you need to be careful when considering the "unlimited" transfer statement as you have to know what the IATA approved routes are. You cannot just hop from one aircraft to another on any old mileage run route you like.

You need to consider items such as the difference between stopover and transfer. Usually a stopover is any transfer of equal to or more than 24 hours, but sometimes it is 4 hours.

You need to consider the maximum permitted mileage.

The route may have the default statement about unlimited transfers but actually be a point to point fare (Say LHR to ABZ does not allow a change in MAN)

You need to consider the higher Intermediate Fare if you stopover on a route.

Not helping much but just beware, you can make an almighty cock-up in assumptions relating to route and transfers.

I wish that helped...