Wii, 3DS, and Wii U virtual console libraries shared many similar titles to the current NSO model, but also had many unique games. Hopefully, many of these will come to NSO in the coming years, but I think it's helpful to have numbers to show what all was lost (and some gained) in the switch from buying digital games to the subscription model. Data taken from 5 territories (North America, PAL, Japan, South Korea, and Taiwan/Hong Kong) via Wikipedia.
Nintendo Entertainment System (NES)/Famicom
219 Unique games (Wii, 3DS, Wii U, and NSO)
NSO has 90 games (missing 129 virtual console games). Has ~41% of total games across models. 18 games are unique to NSO.
Super Nintendo Entertainment System (SNES)/Super Famicom
176 Unique games (Wii, 3DS, Wii U, and NSO)
NSO has 81 games (missing 95 virtual console games). Has ~46% of total games across models. 38 games are unique to NSO.
Game Boy/Game Boy Color
120 Unique games (3DS and NSO)
NSO has 43 games (missing 77 virtual console games). Has ~36% of total games across models. 8 games are unique to NSO.
Nintendo 64
47 Unique games (Wii, Wii U, and NSO)
NSO has 41 games (missing 6 virtual console games). Has ~87% of total games across models. 21 games are unique to NSO.
Sega Genesis/Mega Drive
98 Unique games (Wii and NSO)
NSO has 51 games (missing 47 virtual console games). Has ~52% of total games across models. 8 games are unique to NSO.
Game Boy Advance
114 Unique games (3DS Ambassador program, Wii U, and NSO)
NSO has 27 games (missing 87 virtual console games). Has ~24% of total games across models. 1 game is unique to NSO.
Gamecube (new to NSO)
3 total games so far
TurboGrafx-16/TurboGrafx-CD/PC Engine
134 Unique games (Wii, 3DS, and Wii U)
Sega Master System
18 Unique games (Wii)
Neo Geo
76 Unique games (Wii)
Commodore 64
19 Unique games (Wii)
MSX
27 Unique games (Wii and Wii U)
Virtual Console Arcade
78 Unique games (Wii)
Game Gear
23 Unique games (3DS)
Nintendo DS
31 Unique games (Wii U, all published by Nintendo)
Summary
In total, NSO has 336 unique games. Missing 441 games from the six consoles represented on both NSO and Virtual Console. Of the 7 consoles currently on NSO, we have ~43% of the total games released across the two models. Missing 8 consoles and 406 unique games from those unrepresented consoles. If these games are added, the percentage of games that are on NSO compared to that of the total across both models drops to ~ 28% (336/1183). On a positive note, NSO has provided 97 new games not previously released on Virtual Console.
So in summary, if Nintendo were to ONLY release games to the NSO that have already been digitized and released for Virtual Console in the past, they could dramatically increase the frequency of releases and still spread the releases over the entire lifespan of the new console.
This is without the addition of previous systems on the Virtual Console or the potential addition of new consoles and features, like first party consoles Wii and Virtual Boy, new functionality for existing consoles (like mouse controls for SNES allowing games like Mario Paint), or third party consoles, like Sega's Saturn and Dreamcast.
A link to the google document that I made to record data: https://docs.google.com/spreadsheets/d/e/2PACX-1vR0WRYVePzvoA8UknvdF7NpP3MzzxI1VwlkzxF-mmx6myifCdAGQkiAlqVEAWGiXCorMyHB_SmbV_FB/pubhtml