On this one: Shining Force III Sc. 1 If that's referring to the official Western release, wasn't that a hodgepodge retelling to make the story make sense in one installment without the other scenarios? The list implies that you could play the official SFIII that came out in the West, then go from that into the fan translated Scenario 2 and 3. I don't that's the case?
That's why they have a fan patch for Scenario 1 as well, because the official Western release changes the story and if you are going to play all three scenarios you have to play them as they originally were. That's my understanding. Correct me if I'm wrong and the US SFIII is more accurate than I realize.
Have you checked the file bounds, as in, what happens when the script file is larger than the old one, and what happens if one particular text is long enough to push another one down? Are the script start points hardcoded pointers or some other control values that indicate 'text #001 starts here'? Those were the issues I came across in SOTN, text locations were fixed and all string values used hardcoded pointers (and the values pointing to them were also pointers). The whole script file was a compiled mess, somewhere in the middle of the game code so you couldn't even recompile and pad it out since it would get overwritten by other code, it had a fixed length. Have you checked the file bounds, as in, what happens when the script file is larger than the old one, and what happens if one particular text is long enough to push another one down?