Not only are they probably not operationally prepared to just pull down credit on no notice, but there's an additional risk - the member's VAR calc is calculate

Not only are they probably not operationally prepared to just pull down credit on no notice, but there's an additional risk - the member's VAR calc is calculated using a EWMA (exponentially weighted moving average) volatlity estimate. What this means is that RH can exhaust its entire credit line, and despite allowing no additional buys, their deposite required still increases because volatility went up. Breaching DTCC's requirements with no way to fix the issue.