Danny,
I'm not sure if this partly answers or not, but there is an e.book on the Arnold Scheme on Google Books "The Arnold Scheme: British Pilots, the American South, and the Allies By Gilbert Sumter Guinn".
There was indeed Course 42J, it included C.J Barton VC, who was the schemes only Victoria Cross. It says, amongst other things, a couple of interesting things about the pass rate of the different courses.
Chapter: The Final Six RAF Classes in Georgia
When students of the class (42J) began to fly, Spring was in full bloom and it was good to be alive. For instructors and cadets alike, manoeuvring a Stearman PT-17 with its open cockpit over miles of fields and woods and swamps in the bright southwest Georgia skies was an exhilarating experience.
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Unlike earlier classes, many members of Course SE-42-K had completed in excess of 30 hours flying in flight grading courses at scattered elementary flying training schools (EFTSs) in the United Kingdom. As a result, their progress in primary flying training was much more rapild than earlier classes, and their failure rate much lower.
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The Arnold Scheme: British Pilots, the American South, and the Allies ... - Gilbert Sumter Guinn - Google Books