EDIT: Don't forget to read carefully before you proceed!
"it was only one day's balances. "FSS has not performed any procedures or made any conclusions for activity prior to or subsequent to June 1st, 2018, Close of Business," the firm says in its report."
FSS LLP were allowed to pick a date. And the banks were asked to verify balance on that date. It's not like Tether can go back in time, and put money into the account on the chosen date.