The Registered Number system was a consecutive numbering system used from 1884-1965 to help keep track of the almost 1 million different designs registered by companies in the UK during that period.
The “Registered Number”, usually written as Rd on a tile’s verso, thus provides us with the date when that particular design was registered. Of course, the tile itself could have been made after that date, but typically this helps date a tile to within a few years or better.
The list shown here gives the year and the registration numbers issued during that year. I only show up to 1930 because the style after that does not really interest me that much, but the numbers were used for another ~35 years beyond that. Different websites and different books often show slightly different date and number combinations, but this particular set seems the most commonly published, from what I can tell. It is the list I use when trying to determine the approximate age of a tile.
1884 1
1885 19756
1886 40480
1887 64520
1888 90483
1889 116648
1890 141273
1891 163767
1892 185713
1893 205240
1894 224720
1895 246975
1896 268392
1897 291241
1898 311658
1899 331707
1900 351202
1901 368154
1902 385180
1903 403200
1904 424400
1905 447800
1906 471860
1907 493900
1908 518640
1909 535170
1910 552000
1911 574817
1912 594195
1913 612431
1914 630190
1915 644935
1916 653521
1917 658988
1918 662872
1919 666128
1920 673750
1921 680147
1922 687144
1923 694999
1924 702671
1925 710165
1926 718057
1927 726330
1928 734370
1929 742725
1930 751160