[Pochoir]

Usually thats the lifespan of the artist, say:

Bridge over a Pond of Water Lilies, 1899.
Monet, 1840 -1926

but utterly pointless if the artist in question aint dead

Showing the birth year of the artist is not pointless if the artist is still alive. But it is more commonly expressed as b1982 rather than '1982 - ' I agree. Either way, this is not the case with blue plaques. Have you seen the blue plaques in London? They do not give the lifespan of the resident, just years at the location.