Your question made me go back and look again at nellknits's correction for r23, and as I had suspected in the back of my mind, I had missed something. She altered not just that round but also all that follow, and if I'd followed her entire corrected chart, not just the r23 fix, the double decrease at the beginning of r24 would have worked out just fine. In essence, after adding an MC stitch to the left side of the chart on r23, on r24 and all following rounds she moves one MC stitch from the right side of the chart to the left. So you absolutely can follow her corrected chart if you're more attentive than I was!
(Nellknits, I hope this is an adequate description of your correction.)
That being said, if you want to use my version of the double decrease, which uses two single decreases, you need to do nellknits's fix on r23 but then go back to the chart shown in the pattern and follow it, except for doing the decreases this way on r24:
MC ssk(MC) MC CC MC k2tog(MC) MC round 24
Please let me know if this isn't clear.