assertions

part of exam qn:
You are the external auditor of Tracey Transporters, a public limited company(TT).

Bookings for hire of vehicles are received either over the telephone or via email in TT’s offices.
if customer’s credit rating is acceptable and a vehicle is available, the booking is enetered into the VMS(Vechicle Management System).
Booking information is then transferred to receivables ledger program, where a sales invoice is raised.

audit procedure :
1)For a sample of bookings in VMS, trace details to the list of sales invoices raised maintained in the receivable ledger program.

2)For a sample of sales invoices in receivable legder , trace details to bookings in VMS.

procedure 1, is listed in answer sheet by examiner.
its purpose is to confirm completeness.

procedure 2, is not listed by examiner.
my doubt is , is that a valid prodecure?
in the case of inventory, a similar procedure confirms existence.
here, if i write this procedure , will i get marks?
if right, what reason i should give for this procedure.

thanks.