I suspect, but cannot prove it, that the decisions to upgrade or not, are largely made by airlines a couple of days before the date of flight. They are based on the profile of the loading of the flight to date, taking into account their extensive modelling of last minute turn-up profiles of business passengers who have open tickets.
This comment is principally based on experiences with BA.
No, I wouldn't spend money on these sort of books, which if true would very quickly be disseminated widely and promptly nullify the impact of it being a secret. If it sounds too good to be true ..........