Arijanet Muric, Luka Ilic, Paolo Fernandes and Erik Palmer-Brown have all arrived on-loan this season.
"We now have a larger staff with specialists, such as a sports psychologist and a dietitian. That would not have been possible without City or would have occurred much less quickly. That also has an impact on our own boys, who use it," said Smulders.
He also revealed at the beginning of the partnership, he had to explain to City's players what NAC was all about.
"Now they see: gosh, our Angelino has given his career a boost at NAC and earned a top transfer to PSV. The boys have been training with each other, a number of them have grown up together."