Jim,
I have not studied any where near enough on some matters, some times the info is just not there either. I know this "sunburst" feature is seen on some Japanese swords too, what era I can not comment, so for me it is a case of the chicken and the egg story, someone may drop in and tell me it was the rooster first though.
There are a few images in the History of Steel exhibition where the view presented does not show clearly the "sunburst" but its edges can be seen from the sword profiles.
http://www.arscives.com/historysteel...1/119-k026.jpg
http://www.arscives.com/historysteel...1/122-k009.jpg
http://www.arscives.com/historysteel...1/129-k032.jpg
Gav