Revenues from credit sales may be earned before they are collected in cash do you agree?

Yes, if the product or service is rendered to the customer and said customer has not paid the amount, the revenue has been earned, not collected, to record this transaction you would Debit Accounts Receivable (to show that the service or product has been rendered) and Credit Revenue (income). Once payment is received, then to show money has been collected, you Debit Cash and Credit Accounts Receivable (you no longer have to touch your sales/revenue account as the amount is already listed as being earned).