Answer
Control account figures come from the books of prime entry totals: credit sales from the sales day book, credit purchases from the purchases day book, returns from the returns day books, receipts/payments and discounts from the cash book, and bad debts/contras from the journal. Using totals (not individual entries) keeps them independent of the personal ledgers.
Real-world example The month's sales day book total is posted to the control account, independent of the individual customer postings.