Lucia, so glad someone can understand these things so well. But in this hypothetical situation if the calendar had the image and if getty had a nice strong license with calendar maker (which they probably don't) then this would be an argument for getty, wouldn't it? Or am I getting totally confused here?
Yes. If that images is one whose copyright owner is the calendar maker, the calendar maker is the one who licensed to Getty, and the license is valid and Getty sued you, I think Getty would have a valid claim. The only way to resolve uncertainty about that is to find out if that image is on the calendar, if it is, find out if the license is with Getty.
This is why most people negotiate these things with some level of uncertainty. That's no different from most of life where you need to act based on information you have.
You might be able to gauge whether it's likely the photographer is the one with the license by searching for images by him at Getty. If there are tons, he's probably the one who uploaded and filled out the online license granting Getty permission to list. (This online license may not hold up in court for several reasons. But once again we can't be sure. But we do know the copyright owner needs to fill it out). Of course, there would be no guarantee based on incomplete knowledge. But less incomplete knowledge can be useful.