When Ted's dad helps Barney hit on "Wendy the waitress" it's as if Wendy and Barney never hooked up considering that they are able to pull a lie over her about Barney this is established as happening in 2006 by Ted in the beginning of the episode. However in episode 3.11 The Platinum Rule (2007) when Barney decides to seduce "Wendy the waitress" it is established as happening in November 2005. So this would seem to be a plot hole or continuity error. Unless Wendy is just clueless.