Spanish nationalist side aircraft has as register two groups of numbers: first the aircraft type (that could be share for some unusual types) and follows the number of the aircraft.
Ju-52 was 22 type, so a register or fuselage number could be 22*57 or so on, where * is the black roundel, but I don't know examples of three numbers marks, so I will be happy to see your image.
You can see images of Ju-52 at Spanish Civil War at
http://usuarios.lycos.es/mrvalverde/GC13501.HTM
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Looking for He-59 images, I understand you reference to 577 marks was for this type of aircraft. I found a Image at:
http://usuarios.lycos.es/mrvalverde/HE23216.JPG
Wich shows an He-59 with *529 marks. Later, He-59 will be marked as 71-NN after a roundel, where NN was the aircraft number.
Roberto Pla
http://robertopla.net/