General PC Hardware Sales:
https://arstechnica.com/features/2005/12/total-share/
Spectrum Holobyte (Tetris) Sales:
https://www.google.co.uk/books/edition/Entertainment_in_the_Cyber_Zone/r4M_AQAAIAAJ?hl=en
Mirrorsoft Sales (Tetris) (French Book):
https://archive.org/details/lasagadesjeuxvid0000ichb/page/n5/mode/2up?q=10%2C000
Commodore 64 (Hardware) Sales:
https://edition.cnn.com/2007/TECH/ptech/12/07/c64/
https://web.archive.org/web/20120606052317/http://jeremyreimer.com/postman/node/329
ZX Spectrum (Hardware) Sales:
https://spectrumforeveryone.com/technical/zx-spectrum-models/
https://www.nostalgianerd.com/zx-spectrum-story/
Various Magazines Sourced From:
https://amr.abime.net/review_14924
Additional Website:
https://www.uvlist.net/game-35929-Tetris
Best Sellers:
http://www.guter.org/mastertronic/mastertronic_stats.htm
MSX (Hardware) Sales:
https://www.pcgamer.com/the-bright-life-of-the-msx-japans-underdog-pc/
Nintendo Entertainment System & Gameboy Sales:
https://www.telegraph.co.uk/technology/news/5460283/Computer-game-Tetris-celebrates-25-years.html
https://www.bbc.co.uk/programmes/b0074pz0 (https://www.youtube.com/watch?v=6ohCy4ktA5w)
https://en.wikipedia.org/wiki/List_of_best-selling_Nintendo_Entertainment_System_video_games
https://venturebeat.com/entrepreneur/after-25-years-tetris-has-sold-125-million-copies/
Tengen Tetris Sales:
SEGA Tetris Sales:
https://onitama.tv/gamemachine/pdf/19960201p.pdf#page=12
https://tetris.wiki/Tetris_(Sega)
https://tetris.wiki/Tetris_(Mega_Drive)#cite_note-2
PLAYSTUDIOS (Mobile) Tetris:
https://play.google.com/store/apps/details?id=com.n3twork.tetris&hl=en
EA Tetris:
https://www.ea.com/news/tetris-game-surpasses-100-million-mobile-downloads?isLocalized=true
Wonderswan Best Sellers:
https://swan-of-wonders.weebly.com/sales-data.html
CDi Sales:
https://news.google.com/newspapers?id=IqMaAAAAIBAJ&pg=6614,7897814&dq=philips+cd-i+1+million&hl=en
The Milwaukee Journal. Milwaukee, Wisconsin. pp. D6.