Pete, thanks for suggesting this problem that does bring up interesting philosophical points.
As I see it, there are two slightly different possible answers: either 42257.76 m based on assuming the certified length of the calibration course (1000 feet = 304.8000 m), or 42261.03 m based on using the temperature corrected length of the calibration course as measured by the validator (304.8236 m). Of these, I would go with the second answer, which matches Dale Summers' result, although I don't like the way Dale stated the first sentence of his reply.
Before explaining my reasoning, let's rule out some obvious red herrings. The SCPF is irrelevant because we never use the SCPF in calculating the result of a validation. Also, the fact that the race may have been nominally a marathon wasn't stated by Pete, so is irrelevant. Assuming it was supposed to be a marathon, then by either calculation, it clearly "passes" the validation, as the validated distance is certainly greater than the nominal marathon length (42195 m).
Regarding temperature correction, some basic physics: We normally assume that the lengths of our calibration courses (and race courses) are independent of temperature. The reason for this is that such courses are basically fixed to the surface of the earth, and as soon as you go a meter or two beneath the surface, the temperature is nearly constant year round. While some cracking or buckling of surface roads can occur due to seasonal temperature variations, changes to the course length are negligible, not counting gross events such as earthquakes, landslides, etc. (There are exceptions, of course, such as a course laid out on a bridge, which may undergo greater changes in length when the temperature changes.)
Thus, we assume the calibration course length to be independent of temperature. To understand steel taping temperature corrections, it's just the length of our steel tape (the measuring instrument) which changes with temperature. We assume that the tape was manufactured so its graduations are accurate at a temperature of 20 °C (68 °F). If it's warmer when we do a measurement, we know that our tape is longer than its graduated length, so we conclude that our measured course is somewhat longer than the distance we read from the tape's graduations.
I felt Dale's first sentence to be somewhat misleading because, although correct, it suggests that the calibration course length may vary with temperature. Actually, as stated by Guido Brothers, the cal course length is the same regardless of temperature. But it isn't necessarily 1000.0 ft; that's just the length that the cal course was originally certified as.
Now, the philosophical question: The cal course was originally certified as 1000 ft = 304.8000 m, but the validator found a somewhat greater length of 304.8236 m. Possibly, the validator would feel a little uncomfortable using his own measurement of the cal course, which will make the race course look a little longer. I say to go with the validator's measurement for the following reason: It's the race course, not any particular calibration course, which is being validated. The validator is under no obligation to use the cal course that was originally used in laying out the race course, or any other previously certified cal course. The validator can just as easily pick an arbitrary stretch of road and lay out his own (possibly temporary) cal course to use for the validation. It's nice if the validator can check the cal course used by the original measurer, but this isn't required. In any case, the validator's measurement of the cal course should always be used for calculating the result of validating the race course. Afterward, assuming that the validator checked a previously certified cal course, the question may arise whether to recertify that cal course. In the present case, I don't think any change would be warranted, but if the validator had found the cal course to be shorter than its previously certified length, a change in that certification may be appropriate.
