Electrode potentials vs interfacial potential differences
IUPAC defines the electrode potential of an electrode to be the EMF of a cell in which the electrode in question is on the right hand side of the line representation of the cell and a SHE is on the left hand side.

As such, the electrode potential of the $M^+/M$ couple is

$E^o_{M^+/M} = \phi_{M} - \phi_{R}$

where $R$ refers to the reference electrode, in this case the SHE. This is equivalent to

$E^o_{M^+/M} = (\phi_{M}-\phi_{S}) - (\phi_{R}-\phi_{S})$

Where $\phi_{S}$ is the potential of the solution. Essentially, this means that a relative electrode potential really means

$E^o_{M^+/M} = \Delta \phi_{M^+/M} - \Delta \phi_{H^+/H_2}$

That is, the potential difference of the electrode in question and the solution relative to the potential difference between the SHE electrode and the solution.

It doesn't help the cause that electrochemists refer to potential differences when they use the word potential, however this is just a case of getting to grips with the terminology used in the field!