Updated November 7th: Here are the Scott catalogue numbers:

Sc. 5247-5250
5247 “Deck the Halls”
5248 “Silent Night”
5249 “Jingle Bells”
5250 “Jolly Old St. Nicholas”
5250a block of 4
5250b booklet pane of 20

Updated September 13th: Here are the first-day postmarks for this issue: The Digital Color Postmark for this issue measures 2.27” x 1.45″. The B&W pictorial (rubber) postmark measures 2.99” x 1.70”.

Updated September 3rd:
On October 5, 2017, in New York, NY, the U.S. Postal Service will issue Christmas Carols stamps (Forever priced at 49 cents) in four designs, in a pressure-sensitive adhesive (PSA) booklet of 20 stamps (Item 677300). The stamps will go on sale nationwide October 5, 2017.

In 2017, the U.S. Postal Service celebrates the Christmas season with four new Forever stamps featuring images that illustrate a major theme from four beloved Christmas carols:

• “Jingle Bells,”
• “Deck the Halls,”
• “Silent Night,” and
• “Jolly Old Saint Nicholas.

Familiar lines from each song highlight the individual stamps. The shades of blue in the background of the stamps evoke the evening scenes from the four carols. This booklet of 20 stamps includes five of each design. The late Howard E. Paine was the art director and artist Steve McCracken created the original art for this project.

Availability to Post Offices: Item 677300, $9.80 Christmas Carols (Forever priced at 49 cents) Double-sided Booklet of 20 Stamps
Stamp Fulfillment Services will make an automatic push distribution to Post Offices of a quantity to cover approximately 30 days of sales.

How to Order the First-Day-of-Issue Postmark:
Customers have 60 days to obtain the first-day-of-issue postmark by mail. They may purchase new stamps at their local Post Office, at The Postal Store« website at usps.com/shop, or by calling 800-782-6724. They must affix the stamps to envelopes of their choice, address the envelopes (to themselves or others), and place them in a larger envelope addressed to:

Christmas Carols Stamps
USPS Stamp Fulfillment Services
8300 NE Underground Drive, Suite 300
Kansas City, MO 64144-9900

After applying the first-day-of-issue postmark, the Postal Service” will return the envelopes through the mail. There is no charge for the postmark up to a quantity of 50. There is a 5-cent charge for each additional postmark over 50. All orders must be postmarked by December 5, 2017.

Philatelic products for this stamp issue are as follows:

• 677306, Press Sheet with Die-cut, $78.40.
• 677310 Digital Color Postmark Keepsake (set of 4), $16.95.
• 677316 First-Day Cover (set of 4), $3.72.
• 677321 Digital Color Postmark (set of 4), $6.56.
• 677324 Framed Art, $29.95.
• 677330 Ceremony Program, $6.95.

Technical Specifications:

Issue: Christmas Carols Stamps
Item Number: 677300
Denomination & Type of Issue: First-Class Mail« Forever
Format: Double-sided Booklet of 20 (4 designs)
Series: N/A
Issue Date & City: October 5, 2017, New York, NY 10199
Art Director: Howard E Paine
Designer: Howard E Paine
Typographer: Howard E Paine
Artist: Steve McCracken, Winchester, VA
Modeler: Sandra Lane/Michelle Finn
Manufacturing Process: Offset
Printer: Banknote Corporation of America
Printed at: Browns Summit, NC
Press Type: Alprinta 74
Stamps per Booklet: 20
Print Quantity: 900,000,000 stamps
Paper Type: Phosphor Tagged Paper, Block
Adhesive Type: Pressure-sensitive
Processed at: Banknote Corporation of America, Browns Summit, NC
Stamp Orientation: Horizontal
Image Area (w x h): 1.05 x .77 in/26.67 x 19.56 mm
Stamp Size (w x h): 1.19 x .91 in/30.23 x 23.11 mm
Full Booklet Size (w x h): 2.375 x 5.743 in/60.33 x 145.87 mm
Press Sheet Size (w x h): 9.5 x 11.486 in/241.30 x 291.74 mm
Colors: Cyan, Magenta, Yellow, Black
Plate Size: 800 stamps per revolution
Plate Numbers: “B” followed by four (4) single digits
Marginal Markings: Header “Christmas Carols” 20 First-Class Forever Stamps • Plate numbers in peel strip area • © 2016 • USPS in peel strip area • Barcode

Updated March 13th: The USPS says these stamps will be issued October 5 in New York, which would coincide with the ASDA stamp show.

From the USPS, November 22nd, 2016:

The 2017 Christmas season will be celebrated with four new Forever stamps featuring images that illustrate four beloved Christmas carols: “Jingle Bells,” “Deck the Halls,” “Silent Night,” and “Jolly Old Saint Nicholas. ” Familiar lines from each song highlight the individual stamps. Shades of blue in the stamp backgrounds evoke the evening scenes from the four carols. This booklet of 20 stamps includes five of each design. The late Howard E. Paine was art director; artist Steve McCracken created the original art.