Some records do match an approval process but they have not been submitted for approval. Why?

Some records do match an approval process but they have not been submitted for approval. Why?

Records that are created/modified and match rule criteria of a process after creation of a approval process are the ones that will be submitted for approval.

If you find that records that match the criteria set but are not submitted for approval, it means that they were created/modified before creation of the approval process.