From what i can see its thanks to the script being changed in the actualization normally the simplest way to dismiss this errors are actually a new save file because since this is a linear story you might have missed an event earlier in the game since it was included in might have been included in this patch, try to dissmiss the error and go to lin since it is a lin event it might send you directly to the event or give you another error if it happens like that you most likely might need to either start another game or play an earlier in the game save file, there might be a way to turn the pointer of the "lin_complete15" on manually but that might be harder and even like that there can be more than one pointer missing so its better to go for the try a new save file route might be more tedious but in fact you should be able to skip directly to the choices since you have already saw the history scenes
PS I AM NOT a developer of the game im talking from the experience in other renpy games and the knowledge about coding i have only that