I am not a tax advisor, but when I did my 'add on' through Disney this past March, I noticed something intersting. An 'add on' is additional points with the same use year added to an existing contract. The add on is given a suffix of .00X to your first contract, which carries a suffix of .000. (X, being 1, 2, or 3 etc. depending on how many add on one does). Now, when Disney does the direct debit they simply debit all your loans either on the first or fifteenth of any given month. all at once. Dues too, are combined, and debited as a second transaction. Naturally, an additonal purchase done through resale doesn't work this way at all. In fact, a purcahse done through resale is NOT an 'add on' in Disney's eyes at all. In conclusion, I fully expect to get one 1099 interest expense statement at the end of the year for both of my holdings from DVC.
I can only conclude that Disney will report one combined interest expense to the IRS, hence there would be no way for the IRS to know, or break out the two properties.