This is just speculation, although I have observed this in real life before. A product is made in significant quantity (based on possible product demand)with enough made to fill the supply channel for several years. When supply drops low after several years the product is temporarily reinserted into production, with pricing based on current production costs. This obviously wouldn't apply to products made all the time (MILK?), but a possible NOS coil would fit the profile. It would be interesting to know the production dates of the $54 product vs. the $84 and see if they are typically several years different. Of course, if I had some NOS product I would immediately raise the price to the current level. FWIW