@Chris_Hofer , that is the way it worked before new discussions. Announcements posted before the course is available to students did not send notifications. If the course is published, teacher could use the inbox which will send notifications even if the start date is in the future. We always told teachers to delay announcement posting until the start date (in our school, students normally can't enter a course until the start date). Testing, we found that if students were not restricted from viewing the course before it started, they would get an announcement notification, if their settings allowed it of course.
Maybe some schools allows students to enter courses before they start by default. Many settings in play.
Now we have to test with Announcements Redesign to see what's changed. it's good engineers are aware that using an available from date stops instructor notifications of their own posts, because that needs fixing.