iprice, I understand your point now. You seem to not have a Pandora on your own, just developed the game for it (on another platform), so your only visual interface to PNDs was through the repo website. And from this POV you made everything right, and did not understand "what does this porg guy want".
I on the other side, as a user who experienced PND listings & overviews through various visual interfaces, noted that the implementations of previewpics presentational software (not your responsibility!) do in fact use primary pictures, whereas the PXML previewpic standard does not define a primary picture, and because of that gap between theory and practise, some content may never be seen by users.
I published this issue to a general developer audience (wiki + forum), and notified some affected maintainers. Not with the message that "the maintainers made something wrong", but just to inform, that they are affected from something, which is yet only loosely defined (PXML previewpic), but that nevertheless within that situation, there is a possibility to influence what is shown as the primary picture.
From my side, it is sorted out.
From the PXML team, I hope that they will define a way to reliably set a primary pic, as many presentation contexts only use 1 pic. To get this process started, I wrote the recommendation to the PXML wiki. May experts please follow up and revise it. The easiest would be to define that the image with the filename, which is first in a normal lexicographical order, IS the primary picture, as this is the way most softwares implemented it. I don't see the need for an explicit primary-flag. Just do define the de facto standard as the de jure standard.
And from maintainers who have goodwill meanwhile, they can set an illustrative pic as the de-facto primary pic (first in source code and a filename which makes them first in a normal alphabetical sorting).