  We investigate flux-grown Sm-deficient Sm$_x$B$_6$ ($x < 1$) by global and
local tools, including X-ray diffraction (XRD), electronic transport, and
scanning tunneling microscopy (STM) and spectroscopy (STS). All these tools
indicate a remarkable persistence of the SmB$_6$ local structure in the
flux-grown samples even for nominal Sm concentrations as low as $x=0.75$. As a
consequence, the overall electronic properties of Sm$_x$B$_6$, and particularly
the surface conductance at low temperature, is only affected locally by the
Sm-deficiency.
