I first worked in the City from 1964-1967 and used Bank U'Ground Station daily.
It was routinely awful, packed to the rafters, but you are correct that it worked.
The Northern Line didn't go from Bank to Waterloo but the branch down from Euston to Morden did.
I am not being a clever clogs because my memory failed me and I had to Google and check it out .
On one occasion due to an error I fell asleep and found myself in Morden way south of the river. Happily it wasn't late and I got an immediate Tube back to Chalk Farm and walked the few hundred yards to our flat in Hampstead after a reviving pint in the Sir Richard Steele!
Happy days