NBC ordered 5 more episodes so now Season 5 will have 22 episodes.
from deadline.com:
Blue-collar comedy Superstore continues to be the unsung hero of NBC's Thursday comedy lineup. And in recognition of its solid ratings performance, the network has ordered four more episodes, bringing its Season 5 total to 22.
That is considered a full-season order, and, besides the first season, which was short as
Superstore started off as a midseason replacement, the comedy has gotten full-season orders every year. It is expected to be the only NBC comedy series this season to produce 22 episodes.
It is unclear why
Superstore had a 18-episode fifth season pickup to begin with, but the back order also is a vote of confidence to the series following the showrunner change at the end of Season 4, with creator Justin Spitzer stepping down and Gabe Miller & Jonathan Green taking over.
So far in its fifth season,
Superstore is averaging a 1.2 rating in adults 18-49 and 3.9 million viewers overall in Live+7. It is NBC’s highest rated series on Thursday and the highest rated comedy.