So, there are a ton of resources out there on how unreliable IQ is, and whether it's a valid indicator of general cognitive ability. Instead of linking them, I'll just link to the place that has the most good links: https://en.wikipedia.org/wiki/Intelligence_quotient#Reliabil...

My understanding is that save for general statistical measures of a large aggregate, IQ is a poor measure for an individual (as it has been shown to change quite a bit for individuals over the course of a lifetime).