When Ron grabs his go-bag out of the air duct, there is a note on the back saying that it's specific to "Tammy 1".
In the scene where Leslie and Ann are talking in Ann's office, the computer bag that was a gift from Mark in Season 2 is visible on the desk.
Tammy 1 being a candy striper when Ron was born, she would be at minimum 14 years older than Ron. Patricia Clarkson, who plays Tammy 1, is 10 years older than Nick Offerman, who plays Ron.
Chris Pratt, who plays Andy, keeps a box labeled "The Awesome Album" at his shoe shine stand. Three years later, he would go on to play Star Lord in Guardians of the Galaxy (2014), a character who always carries a cassette tape full of music labeled "Awesome Mix Vol. 1".