The Shadow's stamp of approval

"This is to certify that I have made careful examination of the manuscript known as 'The Living Shadow', as set down by my raconteur, Mr. Maxwell Grant, and do find it a true account of my activities upon that occasion. I have therefore arranged that Mr. Grant shall have exclusive privilege to such further of my exploits as may be considered of interest to the American people."

I recount this familiar statement to delve a bit deeper into a discussion I have going on over at The Cobalt Club. MC Williams stated "As for myself, I always considered Mr. Maxwell Grant as a kind like Dr. John H. Watson. Or....., Perhaps Grant is an actual peudonym and Walter Gibson actually knew The Shadow well enough to be trusted to 'ghost' his exploits."

I feel the same way, however the good doctor was in the stories themselves. Mr. Grant was not. Or was he? Thus my question remains, could M. Grant be Burbank, R. Mann or another recurring character with inside information. I find it hard to believe that The Shadow would sit back after an adventure and recount the details.