By that logic, wouldn't there be another DM206 near Court Sart Junction in South Wales (junction of the Swansea High Street and Swansea District Lines)? How would they be differentiated to avoid confusion - or are they far enough apart that the numbers can be duplicated?
(I think in practice the signals at Court Sart have the PT prefix (Port Talbot), though there must be other instances where there are signals the same distance from Paddington on different routes - for example there will be places on the Berks & Hants, 1835 GWML, Bristol & South Wales Direct and Swindon-Gloucester line which are all equidistant from Paddington).