I think quite a lot of history has been brought to light about the cottages.
If you look back to Mike’s post number 10, which gives info about the cottages, it can be seen that two pairs of semi-detached cottages were built around 1878. This is about 80 years after the tunnel was built. One pair on the hill above the portal, and the other above the cutting at Masshouse Lane/Primrose Hill at High Bridge. The two pairs can be seen on the map, post 14, from Janice.
Historic England mentions cottages 1 and 2, Masshouse Lane, Kings Norton. It shows them just south of the Tunnel entrance, which would correspond to those seen in Mike’s picture post. The other pair at High Bridge could well be 3 and 4 “Tunnel Cottages.” We can see that Alfred Boulton was living in one of the "Tunnel Cottages" in 1901 with his wife and 8 children, and one of his daughters, Asenath, died there in 1967. There are 3 other “Tunnel Cottages” mentioned in the 1901 census, two tug Steerers and tug driver and their families.
The cottages would be quite remote, and as the occupants were involved with tunnel, their history would be linked to it. There is a lot of history that can be found connected to the Tunnel.