As a comparison:
Between the time Pete Sampras won his first grand slam tournament to his last, eight other men won multiple grand slam titles:
Boris Becker
Stefan Edberg
Jim Courier
Sergei Bruguera
Yefgeny Kafelnikov
Gustavo Kuerten
Andre Agassi
Patrick Rafter
Between the time Roger Federer won his first and late (up until now) grand slam, only Nadal, Djokovic, and Andy Murray have also won more than one.