Even with perfect tracking, some buyers use their work email at checkout or pay from a spouse's PayPal. Those sales show up as unattributed, and every report undercounts the ads that really drove them.
The Data cleanup page lists sales and booked or answered calls in the period with no tracked click. Filter by type and value so you focus on the sales that change decisions. If someone with the same first and last name exists, they're suggested. Otherwise enter the other email or phone from your CRM. Attaching merges the records and rebuilds attribution from that lead's clicks within seconds.