As you read this, your AdWords stats from last week or the week before may have changed since you last looked at them.
No, this isn’t some form of AdWords trickery. It has to do with a little known fact that recorded conversions are applied to the date of the ad click, and not the date of the conversion.
So if you were to look at your stats from last week today, and then check on the same date range tomorrow, you might see a different number of conversions.
Data older than 30 days should be stable, as conversions can only be tracked within 30 days of the ad click. So if, for example, someone were to click on one of your ads then purchase 31 days later, the conversion would not be recorded, as this would be beyond the 30 day tracking period.
The bottom line is that yesterday’s conversions may be better tomorrow than today.