I just discovered something interesting! On the blog Shoot First Die Later there has been posted scans from an old article about La notte che Evelyn uscì dalla tomba
. Check it out here:
As I am sure you will notice, the article states that an actress named Anna Mariacher appears in the film, although no one by that name is credited in the film itself. So it is quite possible Anna Mariacher is the real name of the mysterious "Joan C. Davis"! I think there's a good chance that Anna Mariacher is Aunt Agatha. Or maybe she is Polly, the first victim, who features prominently in the pics in the article. I know Polly is supposed to be Maria Teresa Tofano but I am not so sure about this because I cannot find anyone who looks like her in Zeder
(1983), where she is also credited.