There are a couple of inaccuracies in your question and I think clearing them up will help you with the answer to your question.
Given Korean Tang Soo Do is partly derived from Okinawan Karate... And that bunkai for the Katas are relatively recently released to the rest of the world...
From what I understand all Taekwondo is modified Shotokan and Tang Soo Do is the closest to the Shotokan root. This is good because Shotokan has a lot of research material publicly available and Tang Soo Do forms don't need a lot of modification to get back to the originals. Which makes TSD the only TKD branch with real kata application potential IMO. (It's not a dig, I love TKD, but their poomsae are muddled up kata, created to be different to kata for nationalistic reasons, not for holding a fighting art).
Bunkai were not released to the world. The world re-invented it to fill in the obvious gaps like dealing with grasping attacks and close fighting.
There are a small number of Shorin ryu schools and the like who claim to teach karate with full applications as they were handed down, but as of yet I have not encountered anyone making these publicly available. I've personally encountered one such group and their methods are fascinatingly distinct. So much so that I think they are genuine, but of limited relevance to other schools.
Pretty much everyone else has reverse engineered applications or learned from someone else who reverse engineered applications.
Though the concept has always been present, the Karate of Itosu and his peers was not routinely transmitted with a complete set of applications for the kata.
One of the most telling pieces of evidence towards this is the Naihanchi (Tekki) applications of Choki Motobu. They were his own. An article about him told how he enjoyed discussing possible applications for kata. But he was a master of the generation who should have known difinitively, with no need for further exploration.
I believe the truth is that each master taught a few applications in order to drill the skills of fighting, but that after that the kata served as a creative tool for further developing the potential of movement. After all, what more efficient way to train can there be, than drilling one small group of movements (i.e. kata) but being able to use that small set for a vast variety of fighting techniques and tactics.
How do I ask this question without offending anyone?
OK. With greatest respect, how can we ascertain authenticity to the bunkai for the Okinawan Kata's of GM Itosu and others?
Given the amount of counterfeiting that goes on, (I know there are sacred cows here, and I am treading as lightly as I know how)... My skeptical side wants to "trust with/and verify", but how do we know for sure that the bunkai is the real McCoy and not spinning of silkworms?
Its is true because "master told me so", is a logical fallacy called appeal to authority, (this of course doesn't really apply to first hand written testimony of the Kata's author, or testability of assertions made)
I am wanting real answers, because I am considering dropping old katas from my class curriculum, and phasing in new Katas/Hyungs, from the last 80 years to present.
Noboody knows who created most of the kata we have so there is no hope of finding the original applications. Taking into account what I wrote above, for the vast majority of us there is no "Authentic Bunkai". Never was, never will be. The only test is does it work?
That means checking the principles of the technique against the pressures of the real world and it's functionality against a resisting opposition.
But this is not just a point about how knowledge has been forgotten, it is about the fact that the question is wrong.
Bunkai at it's most fundamental is about finding combinations of kihon (basic/fundamental) techniques. Karateka had a hard time understanding kata because we fixed movements with names that limited their potential, and more damagingly our kihon had become limited to block, punch and kick. If your kihon includes these but also has wrist lock, shoulder lock, trap, pull, hip throw, reap etc, kata applications are not that mysterious. You may not spot everything straight away, but you will start to get what is going on more easily.
But this begs the question, if we need to know techniques to find the applications, what do we need the kata for?
The answer has to be that the techniques are not the important part, the sequences of techniques are why we have kata. How and why we should put the techniques together.
Can we apply every sequence in kata as it occurs in the kata and will these cover every combative situation I might encounter?
No we can't and no they won't.
From sequences we get tactics and strategies. These are embodied within a sequence, but transcend the specific techniques.
By having a set of rules (tactics and strategies) that guide us in which techniques to use and when to use them, we can avoid having to train for everything scenario and avoid learning hundreds of set piece drills that we won't be able to get off against an opponent who's not scripted.
So when you consider changing your kata I would suggest you consider whether or not the sequences impart underlying lessons of real value.
That being said I have always felt that TKD should do away with their patterns and create some new ones based on the modern fighting art that they have evolved through both sport and military channels. I think the result would look something like a cross between Ashihara Karate kata and Krav Maga.
