Are U.S. special delivery stamps valid for postage?

The last four U.S. special delivery stamps were issued from 1954 to 1971.

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NATIONAL U.S. POSTAGE STAMP DAY - July 1, 2024 - National Today

U.S. STAMPS & POSTAL HISTORY

Postage stamps and postal history of the United States - Wikipedia

E1//E14 - 1885-1925 Special Delivery Stamps 13v - Mystic Stamp Company

U.S. Special Delivery (postal service) - Wikipedia

Special Delivery Stamps - Guide to Value, Marks, History

U.S. Special Delivery (postal service) - Wikipedia

US Special Delivery Stamps 1885-1971

E6 - 1902 10c Special Delivery - DL watermark, ultra marine - Mystic Stamp Company