They won't tell you what this higher number is under any normal circumstances, and may lie about it, but it probably exists.
If it's small you just have the CEO/founder who decides everyone's salary, if it's a big bigger you have a manager with a margin of negociation but can always get a signoff for a bigger raise by the CEO, and when it gets really big there is a hard grid with categories, ranks within the categories, lower bounds and upper bounds.
In face-to-face communications, those not accustomed to negotiating will often give in just based on misread cues. For example, if someone asks how much you want, and you say a number, stop talking until you get a response. Many beginner negotiators will interpret silence as disagreement (even a short amount of silence) and quickly add "but that number is negotiable".
I have this happen all the time when I'm doing profiles of new candidates, particularly when they are junior. They say "I"m looking for 60K, but I am willing to negotiate". I usually respond by telling them they have already backtracked before receiving any objections.
Practice or get some coaching, and until that time, try to do it via email.