Need someone to clear up my mind about the CP of Pokemon [duplicate]

After playing for a few days, i have some questions about the CP of Pokemons. My friends and i did some tests and here what we got:

1. Im lv18 and catched a magikarp 100CP. My friend is lv18 too, and he catched one with 120CP. We max CP of each one and evolve them. Then the result is my Gyrados has 1469CP and his Gyrados is 1462CP. Only 7CP different not too much.. -> So i think that each lv has a limit CP for each pokemon. That means 2 players with the same level will have the same CP cap. Even if the beginning CP of 2 pokemons is different they still will have the same amount of CP when we max them?

2. On the otherside, another friend of mine catched 2 magikarp. One is 130CP, one is 120CP. He is lvl20. He max the one with 130CP and evolve it into a 1695CP Gyrados. The one with 120CP, he power up it to 130CP, evolve and max it, reach only 1665CP. -> So my idea about the CP cap of each player is wrong? Cuz if my theory is right these 2 gyrados should have the same CP (maybe theres a distance but not too much like this).

Any idea here?