Is there any way to know whether a record was created via the “Make Copy” button? Any sort of log? We are running into issues where users are creating copies of approved bills, which bypasses our approval workflow.

We couldn't find anything in our search. We have users copying Sales Orders and it bypasses any price changes and keeps the Tax Codes from the original order, which also messes up the AvaTax functionality.

Not directly. Best way i've found is to look at the logs for a workflow on that record that has one or more actions that trigger on copy. If the record was copied it will show in the workflow log under the System Information tab with the "copy" context. This requires having logging turned on for a workflow though, which does impact performance a bit.

It does fire a copy action on pageInit in scripting so you could create a custom field and mark it as a copy somehow (like "Replaces X" and have that set as your link back so you know its a copy).

If you add a set field value action on the start state of your workflow that sets the approval status to Pending Approval (on Entry) then that should fix it. Even if they copy an approved one the WF will overwrite with the new value as the new record enters the workflow