This a short theory on how characters attain the
2. The person in question must be a danger to peace (as defined by the World Government standards) i.e. They do not care about damaging islands or kingdoms under the World Government’s protection.
3. The person in question must have a military backing i.e. their own personal army or crew that is also strong. e.g. Jack and Katakuri are both commanders thus they command their own crews aside from been a part of a Yonko crew. They must also have allies (To take on Katakuri or Jack, the Government must be aware of facing the Yonko they are under to and also allies to their crew).
4. The person in question must have fought seriously with a Marine admiral and the Admiral attested or confirmed their strength as tough opponents even for admirals. e.g Marco (although we don’t know his bounty) was able to fight with Kizaru, Aokiji and even Akainu. Although none of the admirals fought all out against Marco, i think it would have been a difficult fight for both Marco and the admiral fighting him.
The reason i brought this up is because of the bounty raise people have been speculating Luffy will have after defeating Katakuri.
Luffy has only met the first and second condition and although he has also met the third condition, the World Government doesn’t know about it.
Luffy has yet to meet the fought condition of fighting all out against an admiral and managing to inflict damage on them that is why he can’t get a billion berry bounty even after defeating two Yonko commanders.
The most possible bounty increase assuming the World Goverment are aware of the defeat of the two commanders is a maximum of 800,000,000 .
*Theory by Misle D Dawn