In 2011, we got a copy of the 6th edition of Fujisawa Hideyuki's 1982 book [LIT. 1] on Igo Hatsuyōron. Neither in his original volume, nor in Go World's English translation [LIT. 2] for problem 120, could we find any hint of a possibly missing Black stone ( 778).
Fujisawa Hideyuki gives only one single concrete score in his commentary. This is two points for Black in his Capture Variation. However, this result is difficult to verify, because he did not show any further sequence for the endgame on the left side. Taking into consideration what is now known to be the best endgame sequence for both, the game ends with four points for Black on the board, if calculated from the problem's setup position.
So we would now like to assume that Fujisawa Hideyuki was well aware of the Black prisoner, taken before the problem starts.