My DS also in 5th took the PSAT 8/9 in Feb. and we have been eagerly awaiting the scores, hopefully, this is a good sign they are on the way.
It looks to me like you are correct with regard to your 1st question.
Just for some additional info...Here is the (last years) Duke TIP 2017�2018 PSAT 8/9 Score Results Summary.
"percentile rankings shown... include only fourth, fifth, and
sixth graders (9,635) who qualified for TIP by scoring in the top 5 percent of standardized grade-level tests�meaning these score results
represent a �best of the best� comparison."
https://tip.duke.edu/sites/default/files/atoms/files/456gts-psat89-results-summary.pdf 
