I wrote to my employer to clarify a date they quoted in the letter they sent, regarding when I need to make a decision about whether or not to return to work. I quoted my union agreement that clearly states that 30 days notice is all that's required. (This is important because at the moment I don't know what job I am potentially returning to in the fall; I have to wait and find out.)
The reply today: Yes, you need to give 30 days notice. Which means mid-July. And: "The reason for the date [we gave you, June 30th] is only for processing purposes. We would like to process all request in a timely manner."
In other words, we make !@#$ up because it is convenient to us. HOPE THAT DIDN'T CAUSE YOU TOO MUCH STRESS.