"I just remembered the date, for whatever reason," he said this week. "November 23, is that right? That got stuck in my mind a little bit. That might be the only one I remember the exact date on."
For what reason? How about because Harbaugh is now in his first season as an NFL head coach, in charge of the Ravens after spending a decade as an assistant with Philadelphia?
The list of people who helped prepare Harbaugh to take over in Baltimore begins with his father, a former football coach. But one of Harbaugh's most influential teachers will be standing on the opposite sideline Sunday. Although Andy Reid didn't hire Harbaugh as an assistant, he was delighted to keep him on board upon replacing Ray Rhodes as Philadelphia's head coach in 1999.
"He's a great football coach," Reid said of Harbaugh. "He could coach any position on the football field and have success with it. He did special teams and the secondary (in Philadelphia), but can coach anything."
Harbaugh has backed up that assessment in Baltimore. The Ravens (6-4) already have won more games than all of last season and are very much a part of the AFC playoff picture despite starting a rookie quarterback and placing an NFL-high 16 players on injured reserve.
Harbaugh learned plenty from Reid, and his education didn't end when he left for Baltimore.
"He's been, obviously, a huge part of my growth as a football coach. I'm proud to call him a friend," Harbaugh said. "We laugh a lot and talk about different things. And he's had some impact; I've called him up when some things have come up here and ask him what he thinks."
Not this week, of course. The Ravens are looking to rebound from last week's 30-10 loss to the New York Giants, and the Eagles (5-4-1) need a win to stay in contention in the NFC East after tying the lowly Cincinnati Bengals last week.
So, while the teacher versus student angle is interesting, it won't be nearly as important as Baltimore's defense containing Donovan McNabb. Or Philadelphia seeking to stop the Ravens' three-pronged running attack of Willis McGahee, Ray Rice and Le'Ron McClain.
"I'm very proud of (Harbaugh), but he and I aren't going to be playing each other," Reid said. "It's our players that are going to be out on the field going after it."
If the Eagles can shut down Baltimore's third-ranked rushing attack, the key for the Ravens will be the play of quarterback Joe Flacco, who grew up in south New Jersey as an Eagles fan and has long admired McNabb.
"That's who I grew up watching," Flacco said. "They've had a good team for a handful of years, and Donovan has been playing really well. For as long as I can remember, he's been a pretty darn good quarterback that takes care of the ball, and it should be pretty cool to have him come into Baltimore and go against the Eagles."
It's been an unusual week for McNabb, who has made headlines for admitting after last week's game that he didn't know an NFL regular-season game could end in a tie.
"It doesn't make me feel bad at all. I was truly being honest," he said. "The thing about it is that now other people are starting to say that they didn't know it either."
His lone focus Sunday will be getting a win - even if it's at the expense of a coach he admires.
"I'm excited for coach Harbaugh. John is a guy who worked extremely hard while he was here and a guy that I talked to constantly," McNabb said. "I'm just excited with the success that he's had over there in Baltimore. For him to go into a new style of play, bring in a coach that he coached with at Indiana (Cam Cameron) and then draft a young quarterback that he can help to develop, it's a great sign for him. He's showing a lot of positive things for all the Baltimore fans."