The IFBB can give a pro card to who ever they want. There is no requirement that you win a contest. If they think that you'll help them make money, then they'll give you a card. But perhaps to give people a reason to enter their amateur championships, they say "the winner of this contest or that contest will get a pro card". But does it really mean anything?
Mohamad Moussawi was living in southern California for years, entering both the NPC USA and NPC Nationals. Then he goes to New Zealand, enters a few contests but fails the drug tests. (the IFBB is suppose to be drug free everywhere outside the US). Now he's a pro, placing 14th in last weekend's Ironman.
Tamer El Shahat competes for Egypt in the World Amateur Championships, and is DQed for failing the drug test. He then wins Musclemania (also suppose to be drug free). Now he's a pro.
Wong Ngai Hong wins his class in the IFBB Asian championships in 99, moves to the US (without the permission of the INS), comes in second in Musclemania in 2000, then enters various NPC contests in New York. Then he competes as a pro in 2004. Unfortunately, his first show was in Toronto and when he tried to reenter the US, the INS said no. Kind of hard to be a pro bodybuilder when you're not allowed to enter the US.
The IFBB in Mexico is suppose to be drug free. Pretty much impossible to win a pro card if you're truly drug free. Might have better luck entering NABBA or WABBA contests, making your mark there, then asking the IFBB for a card.