Should this be considered a duet?? Marvin Gaye and Marvin Gaye on INNER CITY BLUES

[Boogiedown]

Marvin Gaye dueting with himself:



Is it not just as authentic a result of two voices being put together and [singing 'together'] as :



If dueting is simply a matter of blending two voices as was done with Ross and Gaye , why is INNER CITY BLUES, iyo, not technically a duet? Clearly there are two vocal lines there singing in tandem.

Is it necessary for the vocals to be from two different people??

or another way to ask it,
if INNER CITY BLUES, with the two vocals by Gaye singing throughout is not dueting ......what is it??