They are two separate purchases under one membership number, thus you have an original purchase and an add-on purchase, and have the same use year month. As Doc said, the contract numbers will be xxxxx.000 and xxxxx.001 where xxxxx is the same number for both.
Since they are
at the same resort, Disney combines the points when considering all reservations and banking and as far as you're concerned it appears as a single 500 point contract.
However, Internally within
DVC's system it is still two separate contracts. When you make a reservation, bank, borrow, etc. they will do it using points from one of the contracts, or both as needed.
Suppose you have all 500 points available for 2005, and you make a reservation that uses 300 points. DVC will tell you that you have 200 points left. But, internally, they will have used for example the 230 points in the 1st contract, and 70 points from the 2nd contract, so the 1st contract has zero 2005 points left in it while the 2nd contract has 200 points remaining.
As you mentioned, this is important if you ever sell one of the contracts because the points remaining in the individual contracts can be different, even though to you it only shows as having 200 points remaining out of 500.
With a simple call to DVC you can find out how many points are in which specific contract, or as Tom suggested you can get a Points Activity Statement printout which will show all transactions individually by contract.
If you want to sell one of the contracts, it might be possible for Disney to reallocate points between the two. In the example, suppose you made the 300 point reservation, and now want to sell the 270 point contract (which has 200 points available), but want that contract to be the one with zero points and the 230 point contract to have the 200 remaining points. I'm not sure but I think they can reallocate the 200 points over to the other contract. You can call and find out for sure.
Also, in the future, be aware that when making a reservation, doing banking or borrowing, you
can be specific with DVC as to which contract you want to use. For example, I assume you purchased the 230 point contract first and then purchased the 270 point contract. Suppose you still have all 2005 points available and call to make a 150 point reservation. DVC will say you have 500 points, minus 150, leaving you with 350 points, but internally will automatically have taken all 150 points from the 1st contract, leaving you with 80 pts in contract #1 and 270 pts in contract #2. However,
you do have the option that when you make the reservation you can tell them specifically to take all 150 points from contract #2 and not to take any points from contract #1. So in this instance you would still wind up with 350 total points remaining, but internally it would show as 230 points remaining in contract #1, and 120 points remaining in contract #2.
Again, keep in mind for everyone, that when having multiple Add-On's at the SAME RESORT, it is only important to be contract specific when you are anticipating selling one of the contracts and want to control the distribution of the points. There is absolutely NO reason to be specific if you have no intention of selling one of the contracts.
When Add-On's are at separate resorts, DVC will always verify with you which resort's points are being used for a reservation since home resorts have the 11-month booking window.
But again, you can be specific if you want. Suppose you own points at both OKW and BWV. At 10 months you make a reservation at OKW, so in this case the points must be your OKW points since the BWV points are not eligible to be used yet.
However, suppose you make a reservation at 6-months at VWL. In this case you can tell DVC which contract's points you want to use, the OKW points or the BWV points, or you can even split up the points and use some from each contract. Again, you have to be specific.
Finally, suppose you are making a reservation at OKW at 6-months. DVC will automatically use your OKW points for that reservation, and leave your BWV points alone. However, you can instruct them to use the BWV points for that reservation instead. You might want to do this for example if you have tentative plans to bank the OKW points into the next year because you will need them to make a possible 11-month reservation. Again in this situation you would have to be specific that you want the reservation made using your BWV points and not your OKW points.
Hope this all helps.