Reviewing breakdown of sales per key product

“Review the monthly breakdown of sales per key product, compare to the prior year and budget and investigate any significant differences.”

professor my kit states that the above tests Occurrence. So i want to ask three things:

1- how does it test occurrence? My hunch: if sales of a particular key product in this yr are exorbitantly high compared to last yr then the sales may not have occurred at all(fictitious accounting!)

2-can it test completeness too? My hunch: It can, because say if a product’s sales are really low this year compared to prior year then that means the company may have perhaps forgotten to record a no.of sale transactions relating to that particular product, therefore completeness issues.

3- any specific reason why it says “Review the monthly breakdown…”? And not just “Review breakdown of sales”

many thanks professor:) humbled to have you as my tutor!