Same situation.
I was running a completely vanilla game - no mods, no cc, but an older save with two teen characters I had used before.
After getting the patch and Growing Together EP, I started in my post patch testing save, vanilla game. The couple started as teens and aged up to young adult, but never went to prom. For about a week they were able to ask each other and other sims about graduation and they kept saying it was soon and to watch the calendar.
So I kept watching. Meanwhile she became pregnant...still no graduation. Eventually that option to ask disappeared (after a week or so) and I looked then to see if they had graduation certificates. They did not, so I just moved on with their lives.
Down the road...can't say how much later, the certificates arrived in their inventories. I want to note that they don't give a name or any hover text when hovering the mouse or clicking like other similar certificates, like university degrees and lost tooth certificates, birth certificates. They are just generic unconnected objects you have to just remember what they are and who they belong to. Not sure if that is normal.