How do I know whether my numbers are complete?

Every page carries a sync badge showing when the store last synced, and opening it lists each source separately: Shopify, and each ad platform, with its own freshness or a plain note that it is not connected. The dot is amber rather than green whenever a source is missing, because a green dot over an incomplete picture is worse than no dot at all.

The same information drives the attention list on the Overview, so a disconnected ad account is not something you have to remember to check. It appears as an item, with a link to the page that fixes it.