In the 60s it was common at stations in the north west for bay platforms to be numbered with a letter after the number of the through platform to which they were next. Probably the best example of this was Crewe, where before modernisation, what are now platforms 11 and 6 used to be 3 and 4. What are now platforms 7 and 8 used to be 3B and 4B, and what are now 9 and 10 used to be 3A and 4A. It was the same on the island platform where 12 is now, where you had 1, 2, 1A, 1B, 2A and 2B. Similarly the bay platforms at the south end of Preston station used to be 3A and 4A. More recently as trains have got shorter, and platform sharing has become more common, through platforms at many stations have a lower case letter after the number, as at Birmingham New Street, and at Leeds it's been taken a stage further with a, b, c and d used. The exception is platform 4c at New Street, and I'm sure this is a source of confusion to passengers, in addition to all the other confusion created by the more recent reconstruction.