Well, the FAQ tells "You should manually send a retraction and apology to those to whom you reported the spam".
I think it would be more "user friendly" and more efficient to add an option in the report history in order to cancel a report, considering that is a major function.
I remarked also strange things in the reports. Although the FAQ of SpamCop tells we can check or uncheck IP or web adress at the bottom of the report before submitting it, I never saw any check feature.
In general, although I believe SpamCop is very usefull, it lacks options to manage the reports: delete them in a list, check or uncheck spam senders (IP, web, mail adress), cancel report (of course), and probably many other things.
For now, the system is very automatic, but not offer much possibilities of action.
I don't even find clearly an easy way to contact the team of SpamCop. (Only in the forum ?).
In that matter, I think it is too much complex and slow to cancel a report.
I guess it is probably an origin of many errors, and many erroneous additions to the database.