Does an instance of an exclamation point in a WRC 107 report, signifying that the figure name/curve value is exceeded, invalidate the report?

That is up to your decision as an engineer. WRC is set up for a small band of actual situations. If an exclamation mark is given, you're outside the scope of WRC. However sometimes the results are still usable. It depends how far you're outside the scope. Check the range and check if the values given by CAESAR II are acceptable compared to the paper version of WRC107.
Then it's up to you to decide whether or not your calculation is invalid.

Thanks Corne!