MFF
This is also done by Swiss Airlines.
According to JAA you can have up to 2 type ratings current on your licence. Example Boeing 737-200 and a seperate entry Boeing 737-300/900. With my airline we have two seperate LPC checks, one for the 200 and the other for the 300, and one OPC on the 300.
So thay can have Airbus 320 and Airbus 330; Airbus 320 and Airbus 340; Airbus 330 and Airbus 340.