RV NADA values are not established by auction results or retail sales. It is basically an algorythm based on previous values projected forward. There are simply not enough sales yearly to establish those values accurately. Often a year or more may pass without a sale of particular models. Where cars and light trucks record 17 million plus new sales a year and 40 million plus used, less than a half million new RV'S are sold in the very best of years.
There are two thing to remember when looking at book values. No book covering any vehicle will buy your vehicle at its published value nor will they sell you one at that published value. This makes the purported value simply an opinion on any given day. Second, if it were so simple to establish a value as described, dealers would hire High School kids at minimum wage to set their used values. They don't but do pay people very well to invest their money in inventory.
Books are exactly what they are advertised to be...a guide. They are one of many factors that professionals will use to make a well educated guess as to value when making a deal. Sometimes that value proves to be relatively accurate and other times not so much.