I ran the tangents perfectly, or as best as a competitor could without cutting what I thought was the actual course.
And my Garmin had 26.6x. Believe me, I am typically skeptical of Garmins being more accurate than a well measured course with a wheel. And I am aware that most American marathons are faced with traffic control issues that result in typically long courses.
However, this additional length was outside an acceptable margin of error AND the Rock n' Roll organization has a good history of course length errors. This coupled with their lack of ability to offer a clearly defined path for marathoners to follow when running parallel to the half marathoners, leads to the conclusion that all marathoners ran more than the marathon distance (unless they accidentally cut the course).
The first mile was long. And the last mile was long (probably affecting the half marathon as well). And there were some other miles that were long in between. If I missed a BQ or a OTQ by a small margin, then I would be pissed. I certainly let race officials know during the event that the course was not accurate.
In my mind, an accurate course is first and foremost. I know this is not the RnR's priority. I think you have to know going in that you might face such challenges. However, it is still quite frustrating when it substantially long.