Livery Names 

To user/IP address 78.146.90.164,

Mod (modified) is used to show which type of SWT Express livery the unit is in (one conforms with the Disability Discrimination Act, the other one does not),  Not to show each unit has been modified recently with a new livery.  
There is only one type of grey and white livery and only one type of Gatwick Express livery on the 442's so there is no need to put "(Mod at Chart Leacon)".

If you have another reason for puting "(Mod at Chart Leacon)" on other units, please explain here.