The post-mfg argument doesn't resonate with me:
First, since no one really knows how the cards were made, sequencing, etc., it is just as likely that the transfer took place to a blank sheet and the printer did not catch it when the PB sheet was run, or that the transfer could have taken place after the front was printed and then the sheet was fed into a PB back run. Or the printer could have used a blank to clear the press and accidentally reused it in a subsequent run. That is what I suspect happened to generate this card:
Second, and in my mind most convincing, a post-mfg transfer would require that the inks are water soluble once dried. Many, many T206s have been soaked, including by people who post here. Not once has anyone reported the ink running. There are also ample water and liquid stained T206s; where are the runny inks on those? I have numerous examples of wet sheet transfers from various card issues ranging from the T era through the modern era. I have a 1948 Leaf wet sheet transfer:
I've soaked Leaf cards. They do not run. If the wet sheet transfer phenomenon was the result of rewetting I would expect a Leaf card to run. It doesn't.