In some respects they are one contract: You can combine the points at 7 months to make reservations, and your banking percentages are based on the total points you own in both the master and add-on contract. However if you wanted to sell one or both, they are treated as separate contracts. You can even sell off your master contract and just keep the small add-on.
The question people usually ask is, can I combine points to make a reservation at 11 months, and the answer to that is no. For example, if you owned 150 points at SSR and added on 50 points at BCV, you cannot combine all 200 at 11 months to book BCV. At 11 months you can use only your 150 SSR points to book at SSR and your 50 BCV points to book at BCV.