I suspect it muct be very frustrating to pay for a certification and then have it (and your career opportunity) devalued by prolific free information, correct or not.
However whenever anyone talks about the "right" source of information I immediately become suspicious, as I would rather see all ideas presented and let folks evaluate on thier own judgement. "Protecting" people from the "wrong" information feels really weird to me and bad.
However, having gone through MBTI certification, I find much online information, even in this forum, to be more thought provoking and even visionary, than what the standard MBTI text teaches, as it incorporates elements of jungian theory, which MBTI ignores for the most part. I adore the work down by Nardi actually showing the functions.
Because MBTI is used a couple of million types a year, they cannot change rapidly or evolve, without potentially changing the test, and thus placing at risk the historical precedence they have established by 30 years worth of tests being taken and used as a standard for personality assessment. They spend a great deal of time compiling data, albeit with very large error bars, but have sort of trapped themselves into a box by thier own success.
The Step II is interesting as it tries to account for errors in the standard test without really changing it too much.
In reality MBTI needs to change the model to account for evolution of MBTI type throughout adulthood, emergence of the tert/inf functions in middle age, and ideally incorporate elements of the ennegram instinctual variants, as those explain why within one type, you will still see drastically different manifestations of that type.
The only way I can get folks to accept thier MBTI Step II results is to talk about emergence of the tert function due to life experiences or maturaty and how that will result in the results they see in the test.
When testing adults, about 75% of folks test towards thier tert/inf functions, but when asked about their "true" type as part of the consult, will tend to gravitate back to their actual type, but feel unsatisfied until you explain the tert/inf function to them.