1)Ash and Juniper left for Desert Resort. We know this happened for a fact. The next aired episode is Burgh's Gym Battle. Obviously, Ash didn't say to Juniper, "never mind. I don't want to go help save the world, turn this plane around." So obviously these episodes happened before Ash challenged Burgh.
2)Team Rocket was right in the middle of the Meteonite Mission. Were we supposed to think that TR just gave up all of a sudden?
3)Pierce never was seen again. Obviously something happened to him in TR vs TP.
4)Giovanni was heading to Unova. The next time we see him he's at his base in Kanto. Did he just decide to fly back to Kanto out of nowhere.
5)Zager took charge of a now white uniform wearing TR. OBviously something happened to make this occur.
Oh yeah and the preview for the episodes still airs after the Venipede Stampede.