There’s the apocryphal tale of a letter addressed as :
HILL
JOHN
MASS
which was correctly delivered to John Underhill, Andover, Mass
Right, so all you need is the ZIP plus 4. I thought it was cool. 
In his book “The Cuckoo’s Egg” astronomer Cliff Stoll tells of sending a letter addressed only as:
TJ
20016
and it arrived.
My husband has had a letter addressed
Master Steve
<4-digit postcode>
reach him.
These things happen when you live in a town of 300 people