Response to John's Question; from PDGA website:
"How are ratings for an event calculated?
The scores thrown by propagators each round are used to calculate the SSA rating for a specific course layout. A propagator is a current member whose rating is over 799 and is based on at least 8 rounds. As long as there are 5 propagators playing a course layout, ratings can be calculated. The average rating of all propagators will equal the average rating they get for the round – always. If the same course layout is used more than one round, the scores from multiple rounds will be used to determine an overall SSA, as long as the individual round SSAs come out close to each other, so everyone gets the same rating for the same score on the same course. ***If the SSAs are significantly different, likely due to varying wind conditions, the round ratings will be calculated separately.*** If a propagator shoots more than 60 points below their rating, their score will not be used in the SSA calculations."
It seems that the SSAs for the separate rounds were significantly different in this case, and thus round ratings were calculated based on different SSAs which would lead to different round ratings for the same score.