For many games on my game list, the number of hours I am "on record" for playing are much less than I've actually played.
According to Steam, I have not logged any hours playing the games that I poured my time into 4-6 years ago (Half Life 2, CounterStrike: Source, Portal, and others).
But then, my numbers for the game Altitude (bought 2 years ago, did most of my playing in the month or two afterward) are accurate, while my numbers for And Yet It Moves (bought 1-2 years ago) are about 1/10 of what I actually spent.
What determines whether or not Steam keeps tracking my play-time accurately? Are the actual for-real gameplay hours stored anywhere I can get at them?
Is this behavior intentional on Valve's part, something to improve performance? Or have they been struck by accidental data loss on multiple occasions?
Edit: I always launch my games from within Steam, and I never go into offline mode (yay for living with always-on broadband).
For all the example games I gave (and others I didn't), I have logged in to Steam in the past and had it show me accurate playtime numbers. But then, for some reason, those numbers disappear at some point.
Edit: Here is a screenshot from my games list

- Altitude came out on December 4, 2009. I believe the hours played number is correct.
- And Yet It Moves came out on April 2, 2009 (after the March 2009 date mentioned by Anto). I have beat the game, and logged probably 10-20 hours playing it. I believe that the hours on record displayed in the past was correct, but as you can see, it is not correct any more.
