I’m a little confused by this procedure: Inquire of management whether there have been any changes in the key suppliers used and compare this to the purchase ledger to assess completeness and accuracy of purchases.
How will changes in the key suppliers used affect the completeness of purchases?
If a new key suppliers had been added, then you would expect a new account for that supplier in the payables ledger. Ensuring that there is such an account is some evidence of completeness (and to some extent accuracy).