Several years ago several rebacked (or refronted)
T206's hit the mark. The alterations were done well enough to pass the graders and some ended up in numbered holders. What tipped off the collecting community that these cards were frauds was the front/back combinations were impossible. One example was a Mathewson portrait with a red Hindu back. The Mathewson portrait was printed with the first group of subjects in the set and the red Hindu advertisement wasn't used until the 460 series, long after the Matty portrait was discontinued.
It's happening again and interestingly the two examples that have recently come to market are both Mathewson portraits as well.
The first sold on eBay on February 17th. The seller did state in the listing that the card was rebacked. This card was raw and had a Tolstoi back advertisement. This is an impossible front/back combination for this card. The Mathewson portrait was printed with group 1 subjects and the Tolstoi back was not introduced until the printing of group 2 subjects.
eBay Listing
The second recent example sold in the SCP auction that ended on February 29. Again a Mathewson portrait, this time with a Sovereign 460 back advertisement. This is another impossible front/back combo. What makes this card even more troubling is that it is in a TPG authentic holder. The auction listing didn't mention anything about the card being rebacked and stated the following about the authentic grade. "Portions of the black border of the card have been redrawn, resulting in the PSA AUTHENTIC ALTERED rating."
SCP Listing