This mentions the Celsius loan without mentioning that it was overcollateralized and liquidated with no loss to tether (confirmed by tether at the time and by Celsius's lawyers in court filings).
As noted in the article, they announced that the loan was liquidated at a date where the difference in BTC price between when the loan was emitted and the loan was liquidated was greated than the overcollateralization ratio.
As expected, no source on the date, just making up nonsense.
If you'd look at the documents filed in the Celsius bankruptcy, you'd see a sworn affidavit that says Celsius stopped providing additional collateral in May 2022:
>In May and June 2022, Celsius made the difficult decision to forgo providing one of its lenders, Tether, issuer of USDT, a stablecoin, additional collateral and agreed to an orderly liquidation of its loan. During the market crash, Tether issued a margin call to Celsius with regard to an outstanding $841 million USDT loan. Although Celsius had always provided sufficient collateral to support its loan, and had never previously been liquidated by Tether, the Company agreed to an orderly liquidation and settlement of its loan with Tether to preserve the remaining collateral in excess of the value of the loan
Bitcoin dropped around 30% in May-June, so this timeline lines up exactly with the 130% collateralization ratio.
I can give you exact dates, I just didn't bother to look it up. You can see it in this address [1] which is a Celsius-owned payment rail between tether treasury and Celsius trading addresses.
The exact transactions start here [2] (aug 11, 2021). I got the date wrong in my previous post because I didn't remember and was too lazy to check.
As for your misreading of legal documents and misunderstanding of how loans are written:
The loan was not written in May 2022 -- it was written prior to October 2021, when its existence was confirmed. The loan is denominated in BTC at the price at which it was underwritten (early August 2021, BTC price low-mid $40k)
The fact that BTC dropped 30% in may-june 2022 has no relation to the total loan value from Celsius' side. It only changes the amount of collateral tether would be margin calling Celsius for.
Celsius faced a margin call in May 2022 (price 30k) because the loan was written around a BTC value around 30% higher than that (~40k). Note the math checks out here as well.
It took over a month for the margin call to result in liquidation, hence tether's loss of $250-300m at a price of $21k. If tether immediately liquidated in May 2022, they would have skated by without a loss.
If Tether was 50% backed and there was a depeg it would probably be much worse than 50%. Presumably USDT would be redeemed at $1 until Tether's reserves were almost gone at which point Tether would have to stop accepting redemptions and the price of USDT could fall arbitrarily close to $0 in a short time.