Quick question about CP and IV

If you've done the IV's calculations correctly, and they are indeed same CP and different IV's, that's probably because the 89% IV's Snorlax has more Attack stat than the 91%, and since the Attack stat has more influence in the CP formula they have the same CP. Check the Attack stat and let me know, i might wrong but that is the only thing i can think of.

That is basically the purpose of IV's. Aside from its additional bonus stats, Pokémon's with higher IV's always gets higher CP compared to the ones with lower IV's at the same level.

I have 2 Staryu, both are supposed to be level 20

CP 519: Attack 14 Def 10 HP 14 = 84% IV
CP 515: Attack 15 Def 14 HP 10 = 86% IV

How is that possible?

I have 5 Gyrados that I powered up to lvl 32.5
2x cp 2415
Iv 96% 15/13/15 ( hp/atk/def)
Iv 93% 15/14/13
2× cp 2403
Iv 91% 13/13/15
Iv 89% 12/14/14
Cp 2386
Iv 89% 14/11/15

The more atk,the more cp.