Low NADA is retail, for a particular condition. Wholesale will usually be 20-25% below retail, for condition, trade-in values (what dealer is thinking to put into it, not number he gives you as part of a deal which gets mixed up with he makes on what you are buying) may be 30-35% below NADA retail for condition, so he can make something wholesaling it. That's just the way his business works.
Your 55% is relative to MSRP when new? That was likely never a real "value" with 20-30% discounts typical on new TT sales.