A couple of my sources seem to think that the market charter was granted in 1555, and not 1556.

Transcribed from The Comprehensive Gazetteer of England and Wales, 1894-5, and found in uk-genealogy I read that ‘The borough received a charter in the year 1555, during the reign of Queen Mary…’. This mistake is repeated in James Townsend’s 1910 book ‘The History of Abingdon’.

However, most modern sources say the year was 1556. This must appear an unimportant issue to most, but since Abingdon is about to embark on the 450th anniversary celebrations, it does have some importance.