Earlier quoted context omitted.
The collateral requirement was imposed because of the incredibly high chance of the stock simply collapsing again. Trading halts in response to massive movements aren't unusual either.
Was a change in collateral requirement something that was known / codified in some agreement, or was it an ad-hoc decision?
https://www.wsj.com/articles/how-clearing-demands-grounded-t...
WSJ says that it is formulaic.