Tagging omitted, as with any applied coating (read, generally ink) must be fully missing. Any single dot of color or coating keeps the stamp from being "missing ____ ."
That said, pricing is based upon supply and demand. Without addressing supply, demand is exceptionally thin.
The best way to research a price is to review the price lists of the period of the dealer, Alfred 'Tag' Boerger,a specialist in the area of tagging or lack there of. The APS's Library should have a run of them.
After all of that time and effort to find some price you will be best served to list it on
ebay at a Buy It Now price and wait for it to cycle until one of the few collectors of same see it and buy it. I suggest doing the BIN with a make offer option. That will allow you to see what interested folks are willing to pay. It should sell within a few days or after months of cycling.
As to if any are known, I do not have at my disposal information about the missing coating, such that I do not know if it was a here and there issue or if the entire press sheet missed the coating. Here and there is a tough count; a full printing sheet means 99 others could exist as it is unlikely a FDC servicer would get pads of all four pane positions from the press sheet.
You could also contact the Untied States Stamp Society (USSS) to see if you can get detailed information for the luminescence study group.
I will stop here as you need to do some work of your own to earn the reward beyond, "...start at 99c and see what happens...."