In KOD around the time of the battle of Malden, Grady started to tie off his gateways because he was too exhausted (Perrin knows, he wished he could afford the risk to leave the one used by Tam and co. open so Faile could be sent to safety in the TR as soon as she's rescued).

The whole plot point is a bit of a mess. Jordan never properly explained in the first place why Grady and Neald have let themselves get so exhausted by keeping a gateway open and untid for hours every other night (they alternated) for two months, then all of a sudden Grady ties his gateways off to avoid fatigue he can no longer afford. Brandon made it worse by making both Perrin and Grady forget about tying off gateways in TGS, when Grady has done it a few hours before that conversation and Perrin is perfectly aware of this and has noticed the advantages... unless it's Jordan who forgot in his outline that he had had Grady tie off his gateway in KOD, and Brandon followed him into this continuity error. We'll never know.

The general plot point that the Asha'man would get totally exhausted and could eventually not travel for some time (or possibly fight, but in the end they did use their last forces to fight at Malden) was so obvious in KOD that it had to be a built up for what would come next and Brandon is following what RJ had in mind there, no doubt. But it seems that Brandon may have blundered with the conversation between Grady and Perrin about sending the people home in TGS, with the silly calculations that make abstraction of the tied-off gateways solution. It sounds like Brandon missed the detail that the Asha'man know about tied-off gateways but for some reason have let themselves reach the point of exhaustion before they started doing it. Perhaps they misjudged their strength (male pride?) or constantly told themselves "bah, this should be over in a few days". It's even more bizarre because Grady and Neald were shown as careful about not wasting their forces, sleeping extra hours whenever they could etc.

I think Jordan rather intended the two Asha'man after Malden to tell Perrin: now we've reached the point at which we'll be unable for a while to channel safely for more than perhaps the occasional small tied-off gateways - and this is uncharted territory for us, we don't quite know how long it will be before things get back to normal. So if you want to send home refugees, expect it to go very slowly, one person able to cross the gateway at a time etc. and to force the camp to stop for many hours each time we send a group of a couple of hundreds off, so we can untie the gateway once it's over. Perrin was at least two weeks or so away from the Jehannah road (and that's an estimate at Aiel speed, which Perrin won't even come close to...), with no food for more than his original group, so he was in a kind of vicious circle. Ideally, he had to reduce fast the number of mouths to feed each day so the exhausted Asha'man could cope with trips to find and buy food, but if he did use the Asha'man to send people away, they would have no forces left for the food expeditions, and stopping to send people off would greatly increase the delay before Perrin and Faile got near a city and its resources.

The solution to this seems obvious: don't send the Asha'man to fetch food and don't start sending off the refugees. Instead, as soon as there's enough food for a few days send Grady and Neald to hunt for Rand, which they would do slowly if they can't make many gateways a day, but still. Once one of them found Rand, he could send a group of Asha'man and the whole situation would be resolved in a day or a few at most.

It may be what Perrin has done. Grady and Neald may not be with him anymore and they have not returned from their mission to find Rand, for one reason or another (if they went to the BT to inquire about his location when he couldn't be found, they may not even be alive anymore... Grady in particular may have felt the desire to stop to see his wife he has not seen in over 2 months), and this would also have taken place while Rand's location in AD was a big secret and he moved each night. It could explain in part how Perrin got stuck setting camp with Galad on the Jehannah road just a few leagues beyond the border of Altara and Ghealdan, as if he couldn't Travel at all and wanted to hide from the Seanchan. From Mat's POV, we know the ways into Murandy are blocked by big armies. Perrin and Galad both missed (by weeks) the small window of opportunity Mat had opened in KOD - and Tylee had spotted Galad and no doubt reported his location. IMO, the encounter between Perrin and Galad happened after Galad got ahead of Perrin at turned east at the road, figured out the ways north and east were blocked and turned back toward Ghealdan (he has little choices left but to go to the mountain passes Perrin and co. have used in TDR, cross to Almoth and go north and cross into Andor by the passes in the area of Baerlon....). I think Galad bumped into Perrin on the road as the WK were heading back west, and Perrin learned from them he couldn't head east without bumping into large armies blocking the way.

The fact Perrin can Travel and Perrin can help Galad make his deal with the "serpents" for TG would explain why the groups have stopped a few leagues away from the border of Ghealdan, waiting to Travel out of there. But it only makes sense if the Asha'man are no longer with them, otherwise it's been many weeks and there's no obvious reason why Perrin still can't Travel. It's not like camping in the wilderness in Ghealdan with 100,000 refugees is anywhere close to a good situation...