Interesting to read your blog and it may interest you to know that a point shortly after leaving Knighton you will leave the true line of Offa's Dyke, as a archaeological entity and follow a route of convenience that suits those who prefer it to be something else. There are sections of the Dyke marked on the OS map that show it to veer east into Herefordshire and then the old boundary of Mercia becomes the River Wye until the Offa's Dyke Trail re-crosses the river at Hay on Wye. Not having walked it this far south I do not know if the information supplied recognise this.
I discovered this anomaly around 2012, when the CLA published their national policy document on access and our rights of way network. I had been following the rather puerile writings of one Harry Cotterell, who had become the president of this landowner's lobby group, I say puerile because he seems to have concocted a policy on zero input about the history of access and only used biased anecdotes, collected from CLA membership as the basis for publishing a policy centered around trimming the access network under a heading of 'Common Sense'.
The very fact that his family owns an estate of some 2000 acres in Herefordshire, which he claimed to manage the agricultural business, has Offa's Dyke within it and probably that part, where the north section terminates at the River Wye, escapes his notice. Surely landowners should be aware of how their ownership of land that includes parts of our national heritage impacts on the rest of the community.
I hope you enjoy the rest of the trail, this little anomaly may interest you and if you do find any other comments on this, I would be very interested to hear them. Maybe I have the wrong end of a stick, but an explanation why the national trail deviates from the true historic line, without pointing a finger at landowners, who are in denial of the Corruption of the Definitive Map, claim that we have the best access to countryside in the world and advocate trimming out those underused ways, rather than adding in lostways to make them effective, seems relevant.