Coding: codes: how they are used and calculated: suffix codes: form P9X
The use of suffixes allows HMRC to tell the employer to raise certain codes by standard amounts.
Form P9X gives employers a list of the changes needed from a common date. It tells employers which codes to amend by the standard amounts and for which codes they should expect a form P9(T).
The use of suffixes means that you will often only have to review main source codes which have suffix T. The Annual / Budget Business Guidance Notes give full details.