Late notification of marginal items of pay

In CWG2 https://www.gov.uk/government/publications/cwg2-further-guide-to-paye-and-national-insurance-contributions/2024-to-2025-employer-further-guide-to-paye-and-national-insurance-contributions it says 'Occasionally, payroll sections do not get to know about certain marginal items of pay, for example, expenses, until sometime after they have been paid or treated as paid.' The only explanation of what a marginable item of pay is expenses. Can you please give more clarification of what a marginal item of pay is in this context? I dont believe it is for items such as overtime, or backdating of salary say for a pay rise, missed payments for working, bonuses etc - but please clarify if these are included in this terminology, and if not examples of what is.

Hi,
Marginal pay items would most likely be items of pay not considered core item such as the ones you've mentioned like salary, bonus etc.
Thank you.