That's true, assuming there are at least 10 previously rated players of 800 or greater. But the official round ratings are not calculated everyday, only five times a year.I've been told that the only thing that's needed is the player ratings of those playing the round.
When the TD posts scores there is an option to enter a course par, of which might be the same as a previous rounds SSA. The par entry appears to be used to create unofficial round ratings. The official round ratings and the SSA are calculated later.