As I understand it, the limit is not hard coded and fluctuates with the current activity.
So the GPT could say that you have 20 messages left, and then suddenly activity impacts ChatGPT badly and they have to restrict all users more. And then the 20 messages become 2 messages.
Also, I don’t see how they could dynamically implement such a limit… As time goes on, you would get rid of the limits. If you don’t use ChatGPT for 2 hours, when you come back you should get “full” “credits”. It’s hard to show you in real time how the limits, ratios, or quotas evolve for you… at least that’s my vision of the problem.