I suppose, if giant Betta had any characteristics of other Betta forms, I might be cajoled into thinking of cross-clade breeding....but they don't. Although a certain amount has happened and is happening in the wild (evolution), sheer size does not seem to provide sufficient survival impetus to produce large Betta. People provide that impetus. "Mine is bigger than yours." Good one, Tamer.
As in other domestically bred animals, there seems to be a limit to size. Even though the largest Betta, cattle, sheep or dogs are being crossed, each of these animals seems to have been maxed out.
That's why I also have to quibble with Jim Sonnier and others who subscribe to the "giant gene" theory. From the little discussion I've had with giant breeders, their fish don't seem to follow the Punnett square as neatly as do characteristics like color, fin type and scalage.
Having to cross with standard-sized fish, in order to achieve configuration and color goals, really complicates the issue.
As for getting documentation from Asian breeders....ROFLMAO