Test of control for sequence checks

Your choices to consider are:

Reperformance – if the sequence is broken but the missing items have been properly followed up, that will be evidence of the control having been performed by the responsible person. If missing items not followed up, the control has not been performed.
The problem with this is that if the sequence is not broken, that does not evidence that the check was performed.

Observation – as for any test of observation it will only confirm that the control was exercised on that occasion.

Inspection of evidence of the control having been performed – this usually takes the form of approval signature (e.g. on a monthly payroll) or a stamp (e.g. “authorised” on an invoice) or other check mark. If gaps in the sequence of sales order are supposed to be cancelled orders, then perhaps there will be a file of cancelled orders that can be inspected.