Capt. Lewis:
David Baker's short 1990 bio of Bishop relates at page 10 that the meeting between Ball and Bishop occurred on May 5 during a visit by Ball to 60 Squadron. This portion of Baker's book appears to rely solely on Bishop's autobiographical account for its description of the meeting. I am aware of no other reference for the time and place of this meeting. I find no reference to a social visit by Ball on May 5 in Alex Revell's book on 56 Squadron, which recounts other events for that date, including a very intense aerial combat by Ball.
Baker's book is a useful source for the narrative text of Bishop's CITARs. A quick glance through them reveals a number of victories achieved with 50 bullets or less. So his marksmanship apparently was right up there with that of
René Fonck, along with Bishop's other virtues.