Why is The A.T. Guide final mileage different than ATC’s final mileage?

Each year we gather reroute information all during the year and then wait for the ATC to release their final mileage to compare and make any last minute adjustments. This final piece of information comes in at Thanksgiving every year. This is why, while our updates are finished by October each year, the book historically doesn’t ship until mid-January. In 2021 supply chains and print lead times became slower than ever and we had to make the decision to go to print much earlier in order to avoid extraordinarily late shipping dates. This means we have to make our calculations before ATC releases their “official” mileage. We still get the official number from ATC around Thanksgiving. Anything we may have missed we post in the PDF and on our online updates page. A pleasant side effect of this process is the PDF is immediately available for download in November and the A.T. Guide books arrive in time for Christmas shipping deadlines.