The question seems to boil down to a few points
1) Did they know they had drugs in the bag?
1a) Can they convince the judge of that? Even if they say they did not know the judge may or may not believe them.
2) Does this point matter as a matter of law in Japan. I don’t know. The fact that they knew they were doing something illegal may be a problem.
I don’t think there is any argument over if they had drugs or not, I think that is well established.
I feel bad for these boys but I don’t have much hope that they will be exonerated, maybe they can arrange to spend their time in jail in Israel instead of Japan.