Lightning disc had those same four disc names and from what I am hearing might sue prodigy for using them.
That's what I thought you'd say. No, Lightning had some numbered discs, but they did not have a D1, D2, D3, or D4:
Disc Golf Sweden: http://discgolfsweden.se/discar/dis...ufacturer=Lightning Discs&DiscLine=-1&Type=-1
inbounds Disc Golf: http://www.inboundsdiscgolf.com/content/?page_id=431
The Midnight flyers were all numbered too. Discmania has discs that are initialed numbered as well. I don't think anybody is (successfully) suing anybody.