I don't want to ask a silly question like "What is the authoritative
bunkai" -- if there were such a thing, we'd all know it, I'm sure
I disagree that it's a silly question. It is exactly the question which should be asked about the contents of all kata and forms.
Certainly when forms were created, there would have been a single correct interpretation of the movements. The modern concept that there are and were always multiple meanings for movements in forms is a profoundly bizarre one. How could it have occurred, and over so many kata and forms? No, the fact of the matter is there was, and most probably is, a single correct interpretation that fits the movements well, and much of the difficulty we have today in terms of quality within our martial arts is related to the inability to find that correct interpretation.
I also disagree that "we'd all know it". There is generally a lack of questioning of teachers of martial arts, students are particularly credulous. It's typically only after several years and numbers of attempts to use techniques that they begin to question what is being taught. If that process never happens then as teachers they simply pass on the misinformation they have been taught. We end up with generations of practitioners and crucially, teachers, who have been deeply misinformed about the nature of their martial art, and what kata and forms are.
Thankfully today, students and practitioners are beginning to question the techniques which have been passed on to them, as they are tested and fail under pressure.
Example suggestion using a common entrance method:
- The drill sequence begins opponent opposite holding your right wrist/forearm with his left hand.
- uchi-uke "block" catches opponent's left elbow and rotates him clockwise. He ends up facing mostly away from you.
- Right handed "punch" pushes his arm up his back.
It's a very common sequence found in many kata and forms and is a very common restraint/arm lock technique used all over the world. The application may continue further into the sequence, but I think it fits the criteria that it ends the fight at that point. I would start looking for the application of the next drill sequence from there.
It may not. Often sequences extend far further than one initially supposes and one of the more important aspects of analysis is finding the start and end point of applications. A notable example being the bear hug defence and subsequent choke retaliation (okuri eri jime) in Pinan/Heian Sandan which requires the entire second half of the kata; some 12 movements.
Looking at other versions of Seisan than the Isshin-ryu version (Goju-ryu/Shito-ryu/Uechi-ryu) and common to all of them is the double raised fist, similar to Sanchin. It's possible this represents a double grip on the opponent (possible clinch position) and the three repetitions of movements are meant to be taken together with each repetition progressively manipulating the opponent into a different position.
The more movements that an application matches, the lower are the chances that the match is random.
Caveat: It's clear today that kata and forms commonly do have multiple applications "hung" on to the movements. It should also be made clear that there is only one correct primary application, and the additional applications while still a (possibly useful, possibly not) component of the martial art are secondary.