Table 3 shows that 10th and 11th graders do about the same on AP tests, controlling for PSAT score.
Students in 10th grade and earlier should be allowed in AP classes if they have high PSAT or SAT scores, and parents can reference this study to advocate for this.
Note that the study looked at kids who took the PSAT in 10th and one or more AP tests in 11th, and kids who took the PSAT in 11th and one or more AP tests in 12th. It did not look at kids who took both the PSAT and an AP in 10th. So while I agree completely with your conclusions, they're somewhat outside the official scope of the study.
(I'd phrase it as "this study supports the idea that it's PSAT scores, rather than grade placement, that's the best predictor of AP success," but not as "this study says 10th graders with high PSAT scores do well on AP tests taken prior to 11th grade.")
