Langdon:
I refer you to Cross & Cockade Journal, Vol.18, No.3 Autumn 1977. "The Victories of Ltn.
Josef Mai, Jasta 5." by Dr. Gustav Bock. The 12th victory scored on 15 May 1918 was with Fok.Dr.I 139/17. and on 20 May 1918, Mai scored his 14th victory on Fok.DR.I 554/17. On 2 June 1918, Mai scored his 13th victory on Fok.DR.I 592/17. No mention of Fok.Dr.I 152/17. I believe Ed Ferko is misinformed here. He did not indicate any source to support his assertion.
Blue skies,
Dan-San