(Strip Number 6082, Original Publication Date, 16 May 1982)
Panel 1: We start off with a smiling Mike leaning forward as he looks in a large mirror.
Panel 2: As he walks down the hallway, he thinks of musical notes; this is probably supposed to mean that a song is playing in his head.
Panel 3: The strip that appears in most newspapers begins with his joining the family at the breakfast table, smiling with his eyes closed and saying "Ahem!!"
Panel 4: Since no one has commented on whatever he wants them to look at, he asks "Well?"
Panel 5: Elly smiles and asks "Well, what?"
Panel 6: A no-longer smiling Mike asks "Doesn't anyone notice anything?"
Panel 7: An awkward silence ensues as the family stares at an increasingly perturbed Mike.
Panel 8: John sets up the punch line by asking what he should notice.
Panel 9: We get a tight close-up of a bewildered and upset Michael telling them that he shaved.
Summary: Given what we know, the notes won't be about how Mike has a rather nebulous idea of how grown-ups live or about how he doesn't realize that not everyone sees the world how he does; what we will see is either Lynn blathering about how no one noticed that she was growing up or her making a self-serving complaint about how she couldn't keep up with how fast her kids were growing.
ETA: As aprilp_katje pointed out, the notes don't match up with the strip at all well; if they'd accompanied this one, they would have.