A search in the UTexas Chaucer Bibliography database turns up only one record with the keyword 'gentilesse', but the Bibliography is a very recent creation:

 
Search Request: K=GENTILESSE                              Chaucer Bibliography
 BOOK - Record 1 of 1 Entry Found                                     Long View
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 Author:         Saul, Nigel.
 
 Title:          "Chaucer and Gentility."
 
 Published:      In Barbara A. Hanawalt, ed.  Chaucer's England: Literature in
                   Historical Context (Minneapolis: University of Minnesota
                   Press, 1991), pp. 41-55.
 
 Summary:        Chaucer views gentility as a matter of virtue rather than of
                   birth or economics, reflecting contemporary shifts in
                   aristocratic lifestyles.  Italian influences and decreasing
                   military service made it necessary for the aristocracy to
                   redefine superiority in terms of worth.  Assesses Chaucer's
                   views in Gent, WBP, the figure of the Knight, and FranT.
 
 Subjects:       Background and General Criticism.
                 Wife of Bath and Her Tale.
                 Gentilesse.
                 The Knight and His Tale.
                 The Franklin and His Tale.