The phrase "are not commonly seen" is correct and usable in written English.
It can be used to describe something that is rare or infrequently encountered.
Example: "These species of birds are not commonly seen in urban areas."
Alternatives: "are rarely observed" or "are infrequently encountered".
"These people are not commonly seen as heroes.
I like the elegant, uncompromising expression of ideas that are not commonly seen as comic.
The Tu-95 bombers are not commonly seen close to Europe, Janzen said.
Last year's survey found that the freezing start to the year had resulted in an increase in the species that are not commonly seen in back gardens, such as siskins, fieldfares and jays, driven out of the countryside in search of food.
The results from the RSPB's annual Big Garden Birdwatch (BGBW), based on half a million people counting birds in their gardens over a weekend in January, also showed an increase in the species that are not commonly seen in back gardens, such as fieldfares and jays, after a freezing start to the year drove them out of the countryside in search of food.
The classic physical exam finding of a palpable "olive" and the laboratory findings of hypochloremic hypokalemic metabolic alkalosis are not commonly seen [275 279].
Modern military martial art forms, such as Israeli Krav Maga, emphasize quick, crippling or lethal moves at close range, whereas older styles may focus on using weapons such as staves and swords that aren't commonly seen anymore.
Although a native tree growing from New Jersey to Florida, it is not commonly seen growing wild in its natural habitat.
Arms analysts who reviewed a photograph for The Times said the stamp was not commonly seen on ammunition circulating through conflicts.
Furthermore, direct bone-to-hydrogel contact was observed in the majority of implants, which is not commonly seen in this model.
