According to Erza, the results of the experiment were only half of those that were expected. It may be possible of course that this is all that took place during that night. Someone else could have been present during Franklin's 'sleep walking' phase, just like how Franklin was observed during this experiment by Erza, and took the stone when Franklin tossed it to the ground? Or perhaps this outcome goes to show a more realistic point of view, in that it would have been actually impossible to replicate the whole night entirely, and that even the fact that they were able to reproduce it to such an extend is in itself an impressive accomplishment.