Google's reporting matches up the cost of a click with the resulting conversions to the same day as the cost of the click. Google keeps track of this by issuing a 30-day cookie that helps record any conversion resulting over the 30 days from the most recent click back to the day you paid for the initial click. Google does this in order to match up your cost with the leads/revenue so you can more easily measure ROI and cost effectiveness. When you are looking at Google reports that have data less than 30 days old, you need to know your lag history to be able to fully compare new performance data with older data.
Example: You spend $1 on a click on January 1st. The person clicking on your ad goes to your site but leaves after a few seconds. If that person comes back to your site in the next 30 days and converts (purchase, lead, or other action), it will be recorded as a conversion for January 1st. This is also the reason that Google data that is less than 30 days old keeps changing as lag conversions are recorded.
If you want to see your lag conversions (they are also shown in the Finch dashboard reports), log in to your Google AdWords account, go to Reporting, Conversions, Search Funnel, Time Lags, and select First Click.
Read more about lag conversions in Finch's white paper, How do time lags affect conversion tracking?