Did you finish a speaker project with those drivers by any chance? Searching for that driver unit here one only finds this:
http://www.seas.no/index.php?option=com_content&view=article&id=583:seas-kingro4y-mk-iii&catid=66&Itemid=250 Coaxial Driver C18EN002/A Bass Driver L26RO4Y Coaxial Driver Review https://audioxpress.com/article/test-bench-seas-e0060-08-06-6-5-king-coax Bass Driver Review(Not Ro4y, Roy)...
www.audiosciencereview.com
No more detailed on- and off-axis measurements of the finished product, unfortunately — actually there is some on the PDF! But the colors were so faded I could not clearly see… 0, 15, 30, 45, and 60.