I don't know if you know that... / You may not be aware that...
Softer and more considerate way to introduce information the listener may not have. Less pointed than por si no lo sabías. Signals good intentions.
I don't know if you know that the event has changed date.
You may not be aware that she'll also be at the meeting.
I don't know if you know that there's a more recent version of the document.