Thirty-two spot-kicks were taken before the Rams won 14-13.
Curle was “slightly disappointed” Derby’s Bradley Johnson was not involved despite completing the game.
“If he didn’t have to take it because he had cramp, a little bit of clarity might have helped,” Curle said.
He told BBC Radio Cumbria: “I could have said to my players – ‘I don’t want you to take a penalty, be injured’.”
Clarity of the laws
Johnson was injured at the end of the second half of extra time, but was not substituted as the Rams had already made their three permitted changes.
New laws introduced this summer means the number of penalty takers are revised if one team has a player sent off – so, if there are 10 penalty takers on one side after a dismissal, the opposition need only nominate 10 as well.
“I’m slightly disappointed, I’ve only been in the game 30 years but I think when you come to the penalty shootout I don’t think you can get to the 11th man and then be told a player is not taking,” Curle added.
“That’s what the confusion was, we’ve got to know before, otherwise I can just say – ‘He’s injured, he’s injured’ and we only have our best five penalty takers taking them.”
Rams displaying “moral fibre”
Derby boss Nigel Pearson might have had half an eye on round three when Mike Jones smashed in Carlisle’s equaliser five minutes into injury time.
And he was critical of his side for failing to take their chances, with Darren Bent’s first goal of the season their only strike in 120 minutes.
“When it goes to a penalty shootout, you need a bit of good fortune, but what you need is a bit of composure and moral fibre and I thought we showed that,” Pearson told BBC Radio Derby.
“If your yard stick of measuring a performance is having a few boos at half time when we come off because they’ve had a lot of possession, then whatever but we should still be creating enough chances.”
Slovenian Timi Max Elsnik was the Rams’ match-winner in the end, stepping up twice in the shoot-out.
The 18-year-old and winger Max Lowe were given opportunities to impress in an otherwise first-team heavy squad.
“For a young lad to step up and score two penalties is a pretty impressive thing to happen,” Pearson continued.
“There are lots things that you can look at in isolation the players would have gained a positive side to it but ultimately it was about progressing to the next round and we’ve done that albeit in a long-winded elongated, frustrating way but we’ve done it.