The New England Quilt Museum in Lowell, Massachusetts recently showed Bed-Post Corners: Quilts Made for Four-Poster Beds from the Permanent Collection
https://www.nequiltmuseum.org/index.html
The show featured bedcovers with cut out corners...
Shaped to fit beds with posts at the foot as in this period
room from the Metropolitan Museum of Art.
"This feature is found more often in New England quilts than in those made in other parts of the country...."
So I looked through my picture files for cut out corners.
Quilt they showed last year from Henniker, New Hampshire
From a Maine quilt auction
Bet this one's from Maine too
Corner details from the New England Quilt Museum
Above and below from the Rocky Mountain Quilt Shop inventory
On line auction
From Barb of Fun with Barb
Shelburne Museum
Dated 1833, Mary Marden, New Hampshire
Pat L Nickols Collection, Mingei Museum
Doll quilts
Jane Katcher Collection
When one sees a quilt with cutout corners one thinks New England,
but we can guess people made these wherever there were four-poster beds to cover.
From Mollie at Fourth Corner Antiques
Susan Pritchard Kirkwood, Charleston South Carolina, 1837
Collection of the International Quilt Study Center & Museum #2008.009.0001
In looking at chintz quilts I've found quite a few Carolina quilts with cutout corners.
The theory is that western immigrants left their four-poster bedsteads behind along the coast
and bought modern beds without the posts for their new homes.
Indianapolis Museum of Art Collection
This beautiful quilt with a fruit panel could be English...
Like this one from the collection of the British Quilters' Guild
(They had four-poster beds too)
I thought I'd look through the dated quilts file and show some circa 1800 American examples
but this is the earliest I could find
Glazed wool bedcover signed 1815 Lucy Arnold
from the Connecticut Historical Society
1818, Louisa Brigham
(I'm not so sure this is an American quilt.)
1818, signed Turner, Maine Historical Society
Interesting that the earliest quilts have square corners. The cut out is a solution to the problem of bunched up bedding around the bedposts. But apparently it took a while to figure out a fix.