Andrew Pearce has kindly provided me with the three sequences used on each of the telescopes he uses.
I have applied each sequence to the Mar 15 Slooh V image in question and found that all sequences, plus AAVSO, give a Magnitude of 12 or there about. Min is 11.86; max is 11.99.
I will now reply to Andrew with fuller details and share the Mar 15 image with him via Vphot.
Stewart