Used stamps exchanges.

Received a letter from Italy today with two stamps on the envelope, one genuine and issued in 1980, the second a poor forgery of the 2020 Porta Pia stamp design (photocopy or printed on cheap dot-matrix printer). Quite easy to spot the forgery, no magnifier required.
In terms of providing a rating, does it matter if a sender uses a forged stamp on the envelope? Or is the only thing that matters the contents of the letter? And, of course, there is no way of knowing whether the sender used a forged stamp knowingly or not ....

I've emailed scans to the member but haven't heard back (yet). It would be interesting to know whether he used the stamp knowingly or not.

This is something new. Could the postal system have missed this? The most important is the content but the stamps on the cover are also usefull.