In DC New Frontier Hal Jordan doesn’t yet have an Oath, which reminds me of the ridiculously crazy Silver Age explanation of the Oath, where Hal tells Tom that he had three weird adventures and made them into a solemn oath. That makes sense, right?
To me stuff like this is still the real explanation. But what about how everyone uses it? I just explain it the same way how Susan’s private name for the Doctor’s conveyance became the official Time Lord name. Because it’s awesome, that’s why.