Admittedly this troper isn't very knowledgeable about average school workplace policies, but was a photo of Susan kissing Les really grounds for her to retire? For that matter did nothing ever happen to the girl who took the photos? It just feels like the author wanted to end the love triangle as quickly as possible.
One could make the argument that Susan wanted out once she made her move and Les didn't respond. That, plus Susan's having been established as not-exactly stable, it makes sense. Of course, it only really makes sense if you had been a long-time reader, knew about Susan's history with Les and knew about the Love Triangle between her, Les and Cayla. So yeah...
Cody and Owen were introduced as Freshman in fall of 2009. It became a running gag that they looked forward to the annual senior trip as a rare period free of wedgies and food fights, including this year, when they really would be going on said trip themselves. Time Jump confusion? Or does Tom not want to write out his only remaining named teen characters?
The characters don't usually graduate within four years' worth of comics. Wally Winkerbean was a freshman in 1992 but he and his class graduated in 1998. Darin Fairgood's class started high school in 1998 but their class didn't graduate until 2007. And of course Funky's class went from 1972 to 1992 (or rather 1988 despite 90's anachronisms).
Why was Wally's capture kept secret? Here's a fun fact about militants fighting U.S. soldiers. They don't keep it a secret. They get any information they can out of the soldier and announce the capture to the world because they know it's a propaganda victory for them. We can't even assume that the military and reporters kept it quiet (as they sometimes do) to make it easier to negotiate his release because the military had already declared him KIA.