The statement that a variable quantity is "at most equal to $12$" is another way of saying that the quantity is "less than or equal to $12$". That number $12$ only serves as an upper bound. The statement carries no guarantee that there is a case where it does equal $12$.
Perhaps this example makes it clearer: $x^2 \ge -1$ for all real numbers $1$. This is a true statement, which I'm sure you understand. However, there is no guarantee that there is a case where $x^2$ does equal $-1$; an in fact, $x^2$ never equals $-1$.
You may wonder: "Why bother writing $x^2 \ge -1$ when you can write a stronger statement $x^2 > -1$? Or an even still stronger statement like $x^2 \ge 0$, which is as strong as possible?"
Writing strong and efficient inequalities is one of the more important tasks in mathematics. Sometimes it's easy to make the inequality more efficient (as it is for the example $x^2 \ge -1$), sometimes it's quite hard. In fact, writing the "most efficient inequality" is more or less the same as determining the maximal or minimal value of an expression, and this is a hard task in general. Entire chapters in Calculus books are devoted to this subject.