Ok, NH 12 update.
I've done the initial revision from the southern terminus at the Bay of Bengal into Kolkata. Points have been added at approximate locations along the route per what to be access points into various villages etc, using villages and towns as the labels if the online maps don't have any at the moment. Google has had good handful added, however, which has helped.
Just to complicate things, Google claims NH 12 and WB 1 take different routes through/around Kolkata than the other maps do.
Thankfully, this is the longest route in West Bengal, longer than even the circuituous state highways.