In coachstuff, we've decided to use the definition of the number of games from this season that have one or more stats entered into them.
Of course, we could've used other definitions - like games with scores on them, or games in the past etc. But each of these has issues - if you use games in the past - well what if you didn't record stats back for those games? All your averages would be out. If you use games with scores in them - what happens when a manager enters a score only - but doesn't do the stats? All the game averages are out.
The only 'downside' we see to the definition of 'games with stats entered' is the rare case where you might add stats for a game in the future. Then that game would be counted in the averages. But really - why would you add stats to a game in the future. No really, why would you?