Not defending him, but one must ask did he exaggerate? He never publicly stated the nature of any association with the Krays or when/where he met them, if he ever did at all.
The media seems to be responsible for attributing a lot of quotes to him without going as far as putting them in speech marks. Courtney said this, Courtney said that, but never a direct quote, never a reference from the person to whom he was speaking.
I suspect his crime in that regard is to simply keep schtum and let the media build the myth on his behalf, which did his notoriety and income no harm at all.