Lots of people in the past almost exclusively used covert 2nd teams to train their NT players. I hated this about NT system. Probably its still going on but I haven'T been around so I can't say. Even Japan has farm-fresh players on its NT. Guys were caught redhanded double-teaming SPECIFICALLY to boost our NT. They closed the accounts and made the products FAs....and those players are still in the NT system. They do this globally. All the cheater has to do is sign up again and they are right back at it plus the fruits of their labor not lost.
I will join the ranks with MMM as a team devoted only to NT training. Looks like YC already is going that route.