Initially I wanted to write a full fledged text about the topic, but then I've found a decade old article Why the Second Generation of Video Game Consoles Is Really Two Distinct and Separate Generations by Rev. Robert A. Vinciguerra on the archive of their blog The Rev. Rob Times, which more or less encapsulates what I've planned to say...

Therefore I'm limiting myself to short note with few links:

• Why the Second Generation of Video Game Consoles Is Really Two Distinct and Separate Generations
  • discussion on r/gamecollecting under blogpost
  • discussion on r/retrogaming under graphic from the blogpost
• Talk:Second generation of video game consoles#Are Colecovision and Atari 5200 really second gen? - Wikipedia
• Talk:ColecoVision#Generation - Wikipedia
  • TV Gamer Magazine (January 1983) : Internet Archive
  • Video Games - Volume 1 Number 04 (1983-01)(Pumpkin Press)(US) : Internet Archive
  • Video Games Player, Issue 1, Fall 1982
  • Third Generation: 1982-1984 - A History of Home Video Game Consoles - InformIT
• Video game generation between 2nd and 3rd? - Retrogaming Roundtable
• Console Generations: The Missing Videogame Generation - Black Falcon Games