We have received the Pantone swatches and several of these have the words ‘revised standard’ on them. Can you explain what this means, have they changed the colour?

Revised Standard means that the dye recipe has changed since the colour was first established; it may not have been recently. The recipes of some colours were changed to make them more reproducible in the real world so that there were not problems achieving the colour in the factories where the fabric is dyed.
It does not mean that the actual colour has changed as the revised recipe is formulated to match the original for colour under D65, however the swatches are marked up to alert you to the possibility that the colour may be slightly different under another light source.