Yeah those need to be added. As far as when gen would change, that would probably be a fitting answer or at least when Wal-Mart/Best buy stop carrying them.
The only issue I have with that is they will carry stuff until it sells.... I saw gamecube games at a walmart even this past holiday season near me still.... Granted they were crap.... Gamestop will run there buy 2 get 1, and buy 1 get 1 subsequently then shift all stock to a few specific stores until it is all gone.... So the majority of locations will clear out all of their stuff in the same week.... This makes it easier to judge a specific time when it is "Dead" as a current platform.... Also, right after Gamestop ceases carrying a platform is when, traditionally, the prices for rarer games on said console start to rise.... I remember the holiday season when Gamecube games all basically doubled due to that....