Your child is clearly very talented in math. Very likely top 0.1%.
As to determining just how talented beyond that, the ceilings on the PSAT and SAT are way too low to be useful, particularly if taken in the teenage years. Think of it this way. In basketball, a player on the high school state championship team can be in the top 1% of all players, but that gives no indication of whether they are potential NBA material.
The way to determine competition math talent is through the AMC exams, as the entire purpose of that exam series is to eventually find the top 6 math students in the USA. Note that there are other types of math talent, such as research math, but that’s not as easily determined because the opportunities for them are rare (but possible, PM me for details).