To many, including myself, a system is "dead" or "not current" once it's gotten its last licensed retail game. I say "licensed retail" because if you include homebrews, etc the Atari 2600 is still "current". Anyway, it reasons to believe that a successful system would be supported after its successor was released, but one of the longest in that regard was the Nintendo Wii, a system that was half-dead on the Wii U's arrival. I thought "the Wii may be the only system, at least launched post-Crash, where the last game came out a longer period of time after the successor came out than the successor came out to the original system." The last game for the Wii came out on November 5, 2019, 6.97 years (2,543 days) after the Wii U came out. But the Wii U came out just 6.00 years (2,191 days) after the Wii. That's a ratio of 1.16 to 1 or 116%. I would expect a typical successful console's ratio to be about 0.3 or 30%, i.e. if it came out at time 0 and a successor came out at time 10, the last game would be at time 13. Maybe 0.5 for some of the more recent consoles.

Anyway, let's crunch the numbers. A negative number means the system didn't make it to its successor's life, i.e. -20% means that the system only made it 80% of the way to the successor's launch. The dates are: launch -> successor launch -> last game. If only a month is available, the middle date of that month is used (i.e. the 15th for a 28-30 day month and the 16th for a 31-day month) and July 2 is used in the case that only a year is available, that being the midpoint of the year, unless evidence points to a certain part of the year. USA release dates are used.

Atari 2600: Sept. 11, 1977 -> Nov. 3, 1982 -> Mar. 1991. 5.15 years (1,879 days) from release to successor release. 8.37 years (3,099 days) from successor release to last game. Ratio: 164.9% (approximate).
Atari 5200: Nov. 3, 1982 -> May 1986 -> 1986/87*. 3.53 years (1,290 days) from release to successor release. 0.63 years (230 days) from successor release to last game. Ratio: 17.8% (estimated, could be -10.4% to 46.1%)
NES: Oct. 18, 1985* -> Aug. 23, 1991 -> Dec. 10, 1994. 5.85 years (2,135 days) from release to successor release. 3.30 years (1,205 days) from successor release to last game. Ratio: 56.4%.
Sega Master System: Sept. 1986 -> Aug. 14, 1989 -> Oct. 25, 1991. 2.92 years (1,064 days) from release to successor release. 2.20 years (802 days) from successor release to last game. Ratio: 75.4%.
Atari 7800*: May 1986 -> Nov. 23, 1993 -> late 1990. 7.53 years (2,748 days) from release to successor release. -3.15 years (-1,149 days) from successor release to last game. Ratio: -41.8%

https://www.randomterrain.com/atari-...tory-1991.html
*For the 5200, I used Jan. 1, 1987 as the last game as there's disagreement over whether it was released in 1986 or 1987. The game, Gremlins, doesn't show up on sales charts until 1987 but it's often listed as coming out in 1986 so it's probably late 1986 or early 1987.
*NES was launched nationwide by September 1986 but the earliest available date in the USA was Oct. 18, 1985.
*Atari 7800's successor considered the Jaguar, not Lynx, as Lynx was a portable system. Atari intended to release a home console sooner (the Panther) but delays with that project combined with more rapid development of the Jaguar caused the Panther to be canceled. The last game, Midnight Mutants, is listed as Oct. 1, 1990 (3/4 of the way through 1990) as there were several 1990-released games but Midnight Mutants was the last.

I'll finish the rest later.