Do degeneracy-labeling charges generate a symmetry at zero coupling?

Determine the nature of the hypothetical conserved charges whose eigenvalues furnish additional quantum numbers distinguishing degenerate single-particle states in the open bosonic string spectrum, and ascertain whether these charges generate a symmetry of the theory at zero string coupling.

Background

In light-cone quantization the authors find evidence of degeneracies: distinct single-particle states at the same mass level and with identical SO(25) Young tableau symmetry but different oscillator content. This suggests that the spectrum may require extra quantum numbers beyond mass and tableau shape to distinguish states.

They hypothesize that such labels could be eigenvalues of conserved charges. However, they explicitly note that the nature of these charges is presently unknown and it is not clear whether they arise from an additional symmetry at zero string coupling. Clarifying this would illuminate the organizing principles of the massive spectrum.