The 1861 census shows John as the 6 year old son of Thomas H Thridgould, 37, Newsagent,  living in Oxford Street, Mile End Old Town, Middlesex.

The 1881 census shows John, now married, as a bookseller and stationer in King John Street, Mile End Old Town.

In the 1882 London Post Office Directory John Thridgould is listed as a newsvendor at 18 Sidney Street.

In the 1884 London Post Office Directory John Thridgould, stationer was at 18 & 20 Sidney Street.

The 1891 census shows John as a bookseller and stationer at 16, 18 & 20 Sidney Street.

In the 1895 London Post Office Directory John Thridgould & Co are listed as wholesale stationers, newsagents & book sellers of 16, 18 & 20 Sidney Street,

In the 1899 London Post Office Directory John Thridgould & Co are listed as wholesale stationers, newsagents & book sellers of 18 & 20 Sidney Street, Commercial road east, E  -  T A "Thridgould"

In the 1901 census John Thridgould and family were living at 20 Sidney Street - and 18 Sidney Street was unoccupied. He was described as a 45 year old bookseller and stationer, and his son Leonard J Thridgould, 19, was a printers apprentice.

The earliest advertising cards I have seen have divided backs - but with an "Inland only message" suggesting a date before 1906. The address was given as 18 & 20 Sydney Street - and they hac started providing a service printing cards to customer supplied photographs.

Raphael Tuck first published "Oilette" cards in packs of 6 in 1903 and Thridgould, presumably acting as a "wholesale stationer and printers" sold "Oilette" cards with backs appropriate to the 1904-06 period for 4/3d for a dozen packets.

In about 1909 the firm Frederick Hartmann appear to have closed down and this may explain a Thridgould card (from 18 & 20 Sydney Street) advertising a special clearance of Hartmann "Beautiful Post Card", originally for sale at 1d each, at 24 for a shilling.

In the same year Geisen Brothers & Co took on the agency for E. A. Schwerdtfeger & Co, and a Thridgould card (which presumably is no later as it still gives the address 18 & 20) was advertising 300 "Gelatined Easter postcards" produced by "E. A. S." which could represent another special clearance of unsold stock for a firm in difficulty. Geisen continued to sell cards under the E. A. S. logo until the outbreak of the First World War, when Thridgould sold much of the stock, in some cases with references to Germany being obscured with overprinting.

In the 1910 and 1914 London Post Office Directory John Thridgould & Co are listed as wholesale stationers, printers & Christmas card publishers of 16, 18 & 20 Sidney Street, Commercial road east, E  -  T N 7968 Central

In the 1911 census a John Thridgould (55, stationer dealer, born Stepney), his wife, a son (John Leonard Thridgould, 29, printer) and a daughter were living at 2 Lemna Road, Leytonstone, Essex.

Various series were produced - and the "Verse & Motto Series" which included "More that 24 different - all Beautifully Coloures and Printed. Quotations from the Poets" could be brought at 6 dozen assorted for 2/- or 3/9 a gross. As the address is given as 16, 18 & 20 this was probably produced in the 1910-1914 period.

Geisen continued to sell cards under the "E. A. S." logo until the outbreak of the First World War, when Thridgould sold much of the stock, in some cases with references to being printed in Germany being obscured with overprinting.

In the 1915 London Director they were listed under "Post Cards (Pictorial)" at 16, 18 & 20 Sidney Street

Examples of obviously war time cards show that the firm expanded to include No 14 and later No 22 during the First World War.

A quick Google search found details of a catalogue from 1930 giving the address 14-22 Sidney Street.

The latest advertising card I have seen  are for "Clearance Comics" at 4/- a gross - and this was presumably after 1930 as the address had contracted to 16-22 Stanley Street.

The company is listed in the 1946 telephone directory as Wholsale Stationers & Printers of 18 Sidney Street.

By 1951 the company had moved to Curtain Road, Bishopsgate, EC2, and were described as wholesale Export Stationers. (I have assumed they are no longer printing post cards and have not followed them further.)