Then why have an NYC cap? You could just pay all your promising under 20s in line with the 26th highest paid player in the club.
But I think if they aren't in the top 25, then they would have to count against the 'NYC cap' (either as a top20 NYC player, or from the 'other money' allowance to NYC players).
So if they are paid as much as the 26th highest paid player (ie, $70-79k), then they would be eligible to play NRL at that amount, or have to count on the 2nd tier cap. Same story for NYC, they could play at that amount (which would smash the puny NYC cap), or count against NYC 2nd tier (which would even more smash that...).
It kind of works fine IMO. That's why teams pay their most talented 3-5 20s players as top 25 NRL guys, even if they are no chance of playing NRL.
And even if someone else plays 'up', no biggie, they can still fit in the NYC cap anyway.
Dunno if my post makes any sense, makes sense in my mind - but not sure I explained it well (typing in a hurry!)