So what happened to Friday's lunch date w/Mary Norton?
Laura phones Mary to back her up in a lie. Mary asks her to lunch that Thursday, and Laura says, "I can't on Thursday; that's my Milford day." So they arrange to meet that Friday.
Lo and behold, Laura and Alec bump into Mary and her cousin outside the Royal on Laura's Milford day. Her lunch with Mary would have been the very next day.
I always find it interesting that people go off about how the scene with Alec's friend could not possibly be part of Laura's recollection, but they never wonder what happened to that Friday lunch at Mary's. Presumably Laura would have sent her regrets, and neither the doctors' conversations and that Friday don't matter, but I just find it amusing.