No, it wasn't called. The broker would inform me, after executing the trades, (typically after the close on the day of the trade) that they literally could not

No, it wasn't called. The broker would inform me, after executing the trades, (typically after the close on the day of the trade) that they literally could not borrow the shares and would send me a 'sucks to be you' message saying I had to close the position before the end of the settlement period or they would close it for me at the market price on settlement day. IIRC, it was less than 72 hours notice and I was given no option for any amount of money to keep the position open. Since these were thinly traded stocks, there were no options available on them so I couldn't keep it going that way either.