1. A method for manufacturing a plurality of permanent magnet generators adapted for a horological application wherein each generator is rotated by a watch mechanism driven by a source of mechanical energy and where each generator power supplies an electronic circuit operating in a given power supply voltage range, said method comprising a step of manufacturing coils, a step of manufacturing rotors, and then a step of assembling a plurality of stators, each formed of a given number of coils manufactured during the step of manufacturing coils, respectively with a plurality of rotors, manufactured during the step of manufacturing rotors, to obtain the plurality of generators; the step of manufacturing rotors being carried out, with given tolerances, on the basis of data defining a reference rotor; wherein the step of manufacturing coils comprises manufacturing N pluralities of coils, similar within the same plurality and different from one plurality to another, N being an integer greater than one (N>1); in that, before said step of assembling the plurality of stators with the plurality of rotors, a step of classifying the rotors of the plurality of rotors into N classes of rotors is carried out, the rotors of each of the N classes of rotors being selected so that they have a magnetic coupling factor with a reference stator, formed with said given number of reference coils placed in a reference configuration relative to each rotor, which is located within a continuous classification value range which is not superimposed on the continuous classification value ranges of other rotor classes; in that the N pluralities of coils are associated respectively with the N classes of rotors, thus forming N ‘plurality of coils and associated class of rotors’ pairs, so that the rotors of each class of rotors each have a magnetic coupling factor with a corresponding stator, formed of said given number of coils of the plurality of coils associated with the considered class of rotors, which is located in an optimised value range among N optimised value ranges relating respectively to the N pairs, each of the N optimised value ranges being at least partially superimposed with another of these N optimised value ranges; so that a minimum value of the N optimised value ranges is greater than a minimum value of the continuous classification value ranges and that a maximum value of these N optimised value ranges is less than a maximum value of the continuous classification value ranges; and so that the N optimised value ranges lie within a range of values for the magnetic coupling factor corresponding to the given power supply voltage range; and wherein said assembly step is carried out by assembling the rotors of each class of rotors with a stator formed by said given number of coils of the associated plurality of coils with which said class of rotors forms one of said N pairs.