This is a key distinction. Plus codes map to a 14m x 14m square area and aren't aware of things like building units or elevation.
If you live in a high rise apartment, a plus code does not identify you precisely. Sadly to do this you need some knowledge of a structure's internals. It makes sense it's being done on the national level in Japan.
The default +2 plus code is ~14m resolution. But you can add more characters to the end to get higher res. 5 more gets you down to sub centimeters.