One of the main ways of generating postcode polygons is to use OS Code-Point Open and from them generate Voronoi polygons.
This visualization compares the Code-Point Voronoi polygons to postcodes from NRS postcode extract, Which is widely considered the best postcode dataset for Scotland. Scotland is used because we have a CAG (NLPG in the south) extract for Glasgow available for a property comparison of accuracy.
The black areas are where the two datasets agree and the coloured areas are where they do not. For this comparison we can consider NRS to be correct.