You don't know who he's bought
If you think Koeman knew who Onyekuru, Sandro, Vlasic and Gana were I think you'd be mistaken. It's obvious that Martina, Stek and Schneiderlin were Koeman signings. It's likely that Klaassen was also. Koeman also seemed to have a massive hard-on for Rooney and Sigurdsson. Who knows with the others? Yes, it's guesswork but educated guesswork.