I'm currently uploading images in JPEG format to Bigstock, but I would like to add the PNG option as well. However PNG doesn't support IPTC metadata fields (correct me if I'm wrong), such that I still need to upload the JPEG, otherwise I would need to manually enter all keywords and descriptions again.

My theory is, that if I upload a PNG file and a JPEG file with identical file name (but different file ending), their system would recognize that. I would expect the system to show me only one uploaded image and automatically use the keywords&descriptions from the JPEG.

Is that true? Anyone with experience in uploading PNG's?
And what about differences in resolution? I reduce resolutions of my images according to Bigstock's filesize limit. This will usually result in different resolutions depending on the format.

I don't want to try it out, I prefer to ask.