If you have two Use Years, you will have to have two separate master contracts. With two masters, the only way to combine points for the same reservation is to do a transfer. And you can only do one transfer per year.
Of course, this is only true if you need to combine points for a single night. If you want to book one night that costs 25 points using 10 from one contract and 15 from another, you have to transfer.
On the other hand, if you are able book whole nights with each individual contract, the separate reservations can then be linked without need for any transfers.