Our certificates contain the field "Race Name". Call it what they want, in this field.
For "Distance", put in the actual measured distance. It is what it is. If you put the actual distance in, then the timer can extrapolate what the desired distance time may have been, and also publish that time.
With our SCPF, a 5k can already be up to 5005 meters, with a perfect ride. If, in Mark's example, the desired Start and Finish locations result in a measurement of 5002 meters (per standard measuring practice), the course may be an actual 5002 meters (the entire SCPF was used due to non-perfect riding path), or it may be as long as 5007 meters, due to a perfect riding path. So, the relevant question is: is 2 meters a material difference in someone's time?
I agree with Mark, that up to an extra 5 meters is not material when it comes to time. It may be an extra second for the fastest normal runners, or 3 seconds for the sloggers. It is material, however, in a record-setting situation.
For this reason, I believe we should put the measured distance in the "Distance" field.
But, this raises another question - what do we put on the map? The race name, obviously. But, I think we should also put a comment "due to Start and Finish locations being in predetermined locations, actual course length is 5010 meters". This is fair information for the runners to have. We certify courses, and their length. We are not PR for the event that chooses to have an odd-length course, for whatever reason.
(Now, who is going to argue that we certify that courses are at least as long as the advertised course length, rendering my position moot?)