Is it possible the USATF could have an inaccurate course?

I ran the Big D marathon and found a discrepancy of 1 mile. My GPS and Google maps both show the course to be nearly 27.2 miles. I understand there is going to be some differences, but an entire mile? That seems far fetched to me. I checked the map of the course on the USATF web site and found it is nothing more than a hand drawn map. With all of today's technology how can I believe it to be reliable?