The MHoGatA wasn't anywhere near, NTM it didn't have the time to get to the Daivyn and Kaitswyrth before winter.
It did have the time to get to the Langhorne where Duchairn had the tools and materials to build winter quarters, which is where the Go4 evidently wanted it, ie in a central location to respond as needed in the spring.
You may well be right regarding the lack of a coastal high road north of the Bay of Bess, but I expect the southern Harchong quarter-army of the MHoGatA to march from the nearest point of the Sabana River to Dairnyth as if there was one, along whatever connecting tracks if not roads between the towns and villages along the way.
Because of its proximity to the equator and mitigating nature of the gulf, 3 crops a year should be possible so the population density should be rather high, so traffic between the towns and villages should be more than heavy enough to require something approaching a 'high road' even if it wasn't built immediately or simultaneously as designed high roads are.
While Dairnyth isn't or wasn't part of Dohlar, given its major port status, I suspect major land access to Dohlar.
Certainly if I were the duke of Bess or Thorast, I'd want direct land routes as well, given the influence of the dukes, I'd expect the church or the crown to pay for most of the costs.

Given the confusion of the map in Dohlar where a river evidently flows between Lake Sheryl and the town of Paityrstyn and then on to Alykberg via a short high road is apparently colored brown and joined to high roads, while a canal connecting Lake Sheryl with Angel Lake is miss-colored as well, and rivers near each other aren't connected despite their obvious internal economic benefit [more than the focus on foreign trade] and the logic of some high roads is also difficult to fathom.
L
PeterZ wrote:I don't believe Dairnyth has the highway leading into Dohlar. I believe those highways connect whatever city lies at the mouth of the Angel river to Gorath and the Duchy of Thorast. Lyonheart's point elsewhere that Dairnyth was not part of Dohlar argues against easy invasion routes as well as competing port cities.
I am not sure I agree that there is indeed a highway along the Bay of Bess into Dairnyth. If there was one, why was it not used to move the GHoG into Dairnyth to eventually reinforce Kaitswyrth? He got hammered mid summer and no portion of the GHoG was directed to support him. Supply issues or carrying capacity limits could be the driving factor. It could also be that no one wanted to shoulder the expense of a major highway so close to the sea where transport costs were much lower.
There are certainly roads along the coast. I just doubt there is a major highway/highroad that runs along that coast connecting the port towns on the Bay of Bess and the Gulf of Tanshar to Dairnyth.