Yeah, Nadal has to defend 3310 points, whilst Ferrer about 1075, because even if he doesn't go to any ATP 250, ATP 500 tournaments, his points don't drop out, except those that exceed 250 points. He has one 500 and one 300 = 250 + 50 = 300 points dropping. The other 775 points are from Mandatories. The difference between them now is 1465.
3310 - 1075 + 1465 = 3700 points must Nadal do without Ferrer defending any point. 4775 if Ferrer defends all points.
What does that mean actually? Nadal must score 3 Masters titles and win a bunch of 250s and 500s to secure his Best 6. Possibly also good results at the other 2 Masters. He doesn't play at one of them, so the mission gets even harder.
If Ferrer does not go to any 250 or 500, he loses 250 + 50 + 160 = 460 points. The additional 160 points come as the 250 from Buenos Aires will be replaced by 90 from Doha/KL. (Acapulco, Barcelona, Buenos Aires -> Auckland, Bastad, Doha.)
We should be getting used to the fact that Nadal is NOT gonna be 4th seed at RG nor at Wimbledon
I wouldn't be surprised if Nadal is not seeded 4th(or better) even at USO. Anyway, we are in for some interesting QFs(TMS & GS) this year