That sort of thing happens all the time. It is possible new owners knew nothing about such a program when the park was purchased. Sellers sometimes hide those type of contingent liabilities. I have been confronted by previous guests of parks I have bought with all sorts of dubious, at best, claims. Fact of the matter is, almost all promotions end at some point in time.
It is a difficult decision to decide where to draw the line. Many parks have had special rates for certain guests because they are friends, past employees or relatives of the previous owner. Should the new park ownership honor those rates moving forward? Another common example is where the previous ownership has offered some free or discounted nights because a guest had to cancel and forfeit their deposit. After the park has sold, the old owner still has that deposit money and now the new owner is faced with putting someone in a site for free if they chose to honor the previous owner's commitment. Most park owners have to at some point stop giving their product away and start to make money. It's how they are going to be in business down the road. Whenever I buy a park and make the changes I feel necessary to have the park operate the way I want it to, I know I am going to upset some people. Unfortunately, that is just another cost of doing business.