Hi Joel,
I’m completely with you on this topic. Manor House to Harringay Green Lanes is a signposted walk and I do think it should be an OSI. Making the case for such interchanges is a background task which I am progressing at the moment. You could certainly write to TfL and request that they consider adding it. The more people who do so increases the chance that it might happen. There are certainly plenty of journey opportunities that would benefit from it.
Looking at your other coments, South Hampstead to Swiss Cottage is not quite so clear cut. Both lines head out in a similar North West direction so it’s not clear how many people would benefit. In this case, the stated definition of the dotted line, which is to indicate nearby stations under 10 minutes walking distance, is probably justified. They cleverly don’t describe the dotted line as an interchange, but I agree that the distinction between the two is blurred.
As for Woolwich, there are only two stations, Woolwich (EL) and Woolwich Arsenal. The latter contains both the DLR and SE/TL behind the same gatelines. There is an OSI defined between the two stations. The map certainly doesn’t help putting the DLR so far away from the National Rail lines.