Even the 70% backing number is too high. According to the findings of the NYAG:
"Because of Tether’s inability to conduct significant banking activity during this
time, it could not itself hold dollars sufficient to back the hundreds of millions of new tethers that
had entered the market. Until September 15, 2017, the only U.S. dollars held by Tether
ostensibly backing the approximately 442 million tethers in circulation was the approximately
$61 million on deposit at the Bank of Montreal."
"Because of Tether’s inability to conduct significant banking activity during this time, it could not itself hold dollars sufficient to back the hundreds of millions of new tethers that had entered the market. Until September 15, 2017, the only U.S. dollars held by Tether ostensibly backing the approximately 442 million tethers in circulation was the approximately $61 million on deposit at the Bank of Montreal."
https://ag.ny.gov/sites/default/files/2021.02.17_-_settlemen...