The first 10 1400's where fully build and delivered "ready to run" directly from EE plant in UK. the other 57 locomotives where assembled in manufactured in Sorefame (Portugal) using main components (engines, motors, electrical and mechanical parts) from EE but frame and steel works where made by Sorefame using EE original plans and license. Maybe that's the reason for the builder's plates mastery?
Getting that info is a little bit more harder to get, since the SOREFAME (ADTranz later) has closed doors and maybe most of the records and serials are gone/lost. Maybe CP or the National Museum has this records in their archive. Only thing currently easy to get is a list of the actual state of each 1400's locomotive.