Complex sentence: The Exhibition was also the first occasion for which the British Post Office issued commemorative postage stamps, the stamps shown were issued on 23 April 1924, a second printing, with the date changed to 1925, was issued on 9 May 1925.
Split into simpler sentences: The Exhibition was also the first occasion for which the British Post Office issued commemorative postage stamps. The stamps shown were issued on 23 April 1924, and a second printing, with the date changed to 1925, was issued on 9 May 1925.