I understand that 20 cv Hotchkisses (6 cyl. 3485 cc.) were named 620 in 1933 (they overcame the AM80S model), and were re-named 686 in 1936 (so happened to the 617, 6cyl. 3016 cc. 85 cv, that became the 680). So, if this car actually was a 20 cv from 1934, it should have been a 617 or a 620.