Valve is notorious for working on games and then not releasing them. There were several Teamfortress 2 versions which only got leaked and playable in the last few years. Similarly HL 3 was worked on several times since HL2 ep2. But due to the company structure and large scope/expectations for such a HL, first person singleplayer game, every attempt was scrapped at some stage of development.

I can recommend Tyler McViker and gabe follower for two great Valve-Journalists with many insider connections and both fid thousands of hours datamining the engine. Its probably where the article got its informations.