I cant find any info about that proof that Tether is beeing backed by real U.S $.
Tether is a straight up scam as far i can see it, things will be more clear later this week.
Apart from the audit from reputable New York accounting firm Friedman LLP.
https://ftalphaville.ft.com/2017/10/02/2194319/tethers-transparency-update-is-out/That's from March the most recent audit was in October. Do you think an accountancy firm would risk its license by fabricating an audit?
I very much doubt it. If it was truly audited by a reputable firm then the question as to whether or not the USDT was backed should be clear. If that's the case then I guess we could be more at ease knowing that at least part of their claims are true.