Two of them, actually. And they also had a bunch of really good players at other positions, too. So you don't really have to have 100 or so recruits that result in top five classes over the 4-5 years that they cycle in, but about half of them have to be really good. And then you need some stars.Ride a 5* QB like Clemson did.
Coming up with more exact numbers is difficult and predicting who close to impossible, which is why it's easier to generalize about whole classes being potentially very good. There is a reason why Franklin has 12-16+ staff whose sole focus is recruiting.