How did nobody see this before?

Because we were all far too busy basking in the warm glow of early Simpsons, that's why Despite what you may have heard, and despite what I have tried to argue for many years now, The Simpsons' golden age (starting and ending somewhere between series 3 and 10 depending on your personal preference) is not perfect. Writer and current executive producer Matt Selman spotted quite a sizeable continuity error during "And Maggies Makes Three", the heartwarming Season 6 episode that ends with a memorable final shot of Homer's workstation at the plant. Having originally sacked off his job to live out his dream of working at the local bowling alley, Homer is forced to return to the plant and Mr Burns with his tail between his legs after the unexpected birth of Maggie. In typical Burns fashion, he gifts Homer a plaque that reads: "Don't forget. You're here forever." Homer - I'm crying as I type this, tears are clogging the keyboard, THE SIMPSONS USED TO BE SO GOOD - reminds himself why he is actually there in return. Anyway, the mistake in question is quite an obvious one and does make you wonder how nobody has actually noticed before. As you can see from Matt Selman's tweet below, Maggie is clearly visible in the portrait hung on the wall, despite not actually being born yet (as Marge is quite visibly pregnant, and Homer is quite visibly panicking). https://twitter.com/mattselman/status/1037147366564851712 Good news though, as showrunner Al Jean took the swift action necessary, promptly (joked about) firing 17 employees. https://twitter.com/AlJean/status/1037202449893941248 Fortunately, one fan had the perfect explanation for the gaff, citing a Comic-Con scene featuring Xena: Warrior Princess: https://twitter.com/Rewster7/status/1037198349663920128 (Or it could just have been baby Lisa. They are related and have exactly the same hair. But whatever.) Regardless, there is another instance of The Simpsons timeframe completely going out the window in the same episode, as you can see in the shot below. This time it is clearly Lisa on the wall, but you will notice that Homer still has a full(ish) head of hair, meaning that this was before the birth of Bart. In fact, this is the exact scene when he finds out about Marge's first pregnancy and the impending arrival of "the boy", as he runs upstairs to hide in the bedroom and pull his hair out. If the above does actually irritate you, then, well, I'll just leave you with one final scene. https://www.youtube.com/watch?v=h1nD4o3zTfo