They were originally boxes and when the short call got exercised he would re-hedge the missing piece with a buy-write and sell the stock out just leaving the short call. Thought the buy-write would conceal the attempt to just short the call. Yes, they are similar to the Jeff Wolfson case where there were multiple unable to locate failures. Those were initially boxes as well. They pretty much all come down to short calls in HTB names and the rise and repeat - re-hedge with a short call. Feldman the oX customer got off - the firm was tagged and the folks who had oversight lost their jobs and one was barred for life. The thought process was the firm facilitated it. The ALJ tagged Feldman as well and then the higher court overturned it.
That is why no firm will allow it. You may get the first short call done, but the re-hedge after the call get's exercised and an inability to locate occurs twice will trigger a SHO violation. Most firm won't allow the first call sale even if it's part of a more complex strategy.
In Wolfson - in addition to paying the profits back there was a $2.5Million fine and a year suspension. Then even after the suspension was served no firm wanted to do business with him. Also, keep in mind the disgorgement is not tax deductible whereas the initial profits were taxable so add another $4 -$5 million to the cost + seven years of legal fees.
In Wolfson his brother did the same trades as well and the size was smaller, but they both got tagged.