Peter’s realization in this issue was probably a good enough answer at the time.
Amazing Spider-Man (Vol. 1) #150
Published: c. August, 1975?
Cover Date: November, 1975
“Spider-Man… Or Spider-Clone?”
Writer: Archie Goodwin
Artist: Gil Kane
Inker: Mike Esposito and Frank Giacoia
Letterer: Joe Rosen
Colorist: Petra Goldberg