Captain Grazer's name is spelled "Bryan" on his office door. It was spelled "Bryon" in Alien Nation (1989).
Matt's case project "The Origin and Spread of Supernova in LA" is dated December 26, 1999. However, several days earlier, a sign in the police station said that there were only five days left until 2000, meaning that the date was December 27, 1999.
While some real-world items are represented by something similar in the Portal "world", others are clearly not. The Portal is repeatedly explained as an illusory projection where everyone sees something different and has no "real" substance. The plank that Jennifer kicks off does not necessarily have a counterpart in this illusion, and having more experience, she could have learned to manipulate the illusions to her liking.