First time the name Galaxy was used by a german LFS for the Itaituba (P14) rays with additional small spots between the larger spots. Here is the link showing a pic of this first Galaxy (this ray is now in USA, hi Mike):
http://www.amazon-exotic-import.de/Gallerie/Rochen/Seiten/Potamotrygon%20spec.%20P%2014%20var.%20Galaxy.htm
Where the name Galaxy Royal was first used is not clear. I remember when Frank and Nico came in my cellar and saw Tess they spontanous said "Wow, a Galaxy Royal".
You all know Tess from my pictures, here is a new picture of her:
Tess has some large spots (the bigger ones have eye diameter), so you could say Galaxy Royal are Itaituba ray with many and large spots. (But be aware, leopoldi x itaituba hybrids show these large spots too, but Tess is pure blood)
The term Galaxy Royal is even used for Itaituba ray with many small spots, like the one royalray has:
But nothing is set in stone. Maybe we should count the dots
normal Itaituba < 400 dots
Itaituba Galaxy 400 - 600 dots
Itaituba Galaxy Royal > 600 dots
btw. Tess has > 800 dots