That wasn't a typo in today's review: Egghead really was created in 1965, not 1966, as evidenced by the date on Jan Kemp's original design sheet:
Egghead's Season 2 debut episode aired on October 19, 1966, with the second half airing the next day (as was the style at the time). By Season 3, the episodes were more standalone, but Egghead still appeared in an uncommon two-parter: "The Ogg and I" (Episode 8) and "How to Hatch a Dinosaur" (Episode 9) However, in a rare double-whammy, that was actually meant to be a three-parter! His third appearance in the season, "The Ogg Couple" (Episode 15) introduces characters who had already appeared in the earlier two episodes, and the only thing that keeps it from ending in a cliffhanger is a bit of voiceover narration obviously edited in later.
But at the same time, Episode 15 has some subplots that pick up directly from things that happen in Episode 8, and others that lead into Episode 9. There's quite a bit of recycled footage among the three episodes, too. It seems like the original script was chopped up and rearranged into just two parts, but then the excised material was re-assembled into a third episode at the last minute?
Or in other words, Egghead's arc in Batman Season 3 got... scrambled?