[Seaplanes]

Please remember that the two He 51 prototypes, He 51a and He 51b, both were delivered from Heinkel in February 1934, at a time when this way of designating prototypes was still common. Later Versuchsträger (test aircraft) were given designations with the letter V followed by a number.
Like He 51V-6 D-IBYI W.Nr. 995 was actually a D-version production aircraft and the He 51V-7 D-ILGY W.Nr. 1485 was actually a He 51C production aircraft.
The series production of the He 51 did not start until
a year later, in February 1935. In addition to Heinkel in Rostock-Marienehe, the factories of Arado, Erla, Fieseler and AGO were all involved in the final production that ended in May 1937.
All repair and maintenance statistics I have seen, all at Bundesarchiv-Militärarchiv in Freiburg, list the He 51C as the main land-plane version. Actually they do not mention the A and B version at all. He 51D being the
float-plane version built in 33 examples.