I think what you are seeing is the normal resale after a product has been around a few years. One good thing about a preamp, unlike dacs, streamers, etc, there is no reason to really upgrade unless there is a feature one is dying to have (assuming you like how it sounds). How much additional improvement can be added after 3 or four years in the analogue realm? Assuming the replacement is in the same price range. Manufacturers update products to keep their line “fresh” or due to parts availability and visual appeal. Plus, new products get reviews in all the audio outlets. One more thing, the BHK series was released during the retail outlet era of PSA. Prices ad discounts were all over the place. A new version within the direct sale method will likely help PSA retain some higher used values.