Oct 20 2019, 9:31pm
"...Smeagol thinks they have come out of the South beyond the Great River's end: they came up that road. They have passed on to the Black Gate, but more may follow"
Note also that the spot where Faramir's company ambushed the Haradrim was well north of the Morgul road as well. Why these troops used the Morannon is unclear; but it probably is simply that the Morgul Pass was wider and flatter than Cirith Ungol but still too narrow and steep to move significant bodies of troops through. The Witch-King's army didn't come through the pass when the signal went up; it was already inside Morgul, on the west side of the mountains.
(This post was edited by Solicitr on Oct 20 2019, 9:33pm)