In 1863, die numbers were introduced on the reverse of sovereigns. This was done to assist with production and quality control, and the practice continued on most London Mint sovereigns. These are located between the wreath and the rose on the bottom of the reverse.
Also, a small quantity were issued with an obverse die number "827" in raised numerals on the truncation of the neck. These are rare, but exist in at least two varieties, the first without reverse die number, and the second with reverse die number 22.
Young head of Queen Victoria facing left wearing ribbon (double fillet) in her hair; the hair is collected up into a knot behind; around, the legend VICTORIA DEI GRATIA (Victoria, by the Grace of God); the designer's initials W.W. (for William Wyon) are incuse on the neck truncation.
In the field below the neck truncation, the date 1863.
The Ensigns Armorial of the United Kingdom within a plain shield quartered with the arms of England (1 & 4), Scotland (2) and Ireland (3), surmounted by a crown. A branch of laurel is shown on each side of the shield, tied at the bottom by a ribbon. At the bottom, the Thistle, Rose and Shamrock (symbols of Scotland, England and Ireland respectively) are placed with a small flower stop on each side.
Around, the rest of the monarch's legend (continuing from the obverse): BRITANNIARUM REGINA FID: DEF: (Queen of the Britains, Defender of the Faith).
No die number on the reverse of most 1863 coins, then die number introduced (located between the ribbon beneath the shield and the rose).
Known die numbers (as per Marsh 2017): 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24 (25, 26 and 38 not confirmed).
Type IA by Marsh (no die number), or IB (with die number on reverse).
References to additional information:
[Book] Remick, Jerome. The Guide Book and Catalogue to British Commonwealth Coins, Regency Coins and Stamps Ltd, Winnipeg, Canada, 1971, p258
[Book] Marsh, Michael A. The Gold Sovereign. Cambridge Coins, Cambridge, UK, 1980. (2017 ed. pp 27-40)