I even looked it up (see link below). Delta cannot get a FAA airworthiness certificate until they have verified that all the ducks are in the row paperwork wise for all maintenance and repairs for the life of the aircraft, and the aircraft is currently in a condition for safe operation.
That is called an export CofA, usually issued by a DER of the registry where the aircraft is leaving. As DL is both a Brazilian and FAA maintenance organisation I would not be surprised they have DERs in house that can do this.
I'm quite sure that takes some time to audit the records and be sure that there are no gaps, and if there are gaps to redo the maintenance with appropriate documented repairs, and to transfer the records into Delta's data base.
This is standard a CofA inspection, all FAA ADs will be done, and all compliance with FAA regulations performed. The aircraft is then placed into the normal DL phase inspection process, the same process is done for a new aircraft.
In the meantime Delta can be doing other repairs, interior changes, and painting the aircraft; none of which needs to be reported as the aircraft does not yet have an FAA Airworthiness Certificate.
You are therefore claiming the aircraft is stateless without regulatory oversight and DL in its capacity of being a Part 121 and 145 maintenance organization doesn’t need to follow its own procedures. Rather bold statements to make.
Since the aircraft came from out of country, it did not have a previous FAA Airworthiness Certificate to report things under.
The aircraft were flown to the US with Brazilian registration. DL has FAA Part 121 and 145 maintenance certificates, and Brazilian Part 145, I don’t see how your claim of being able to do unreported work on the airframes comes from.
It makes life simpler for Dela if the actual title transfer occurred after the aircraft landed at the maintenance base for the in-processing of the aircraft.
The aircraft are leased.
It does not apply to routine maintenance done to defects or wear within the OEM limits that are repaired in accordance with manufactures directions.
Then DL must be doing something very wrong, as most of the entries in the A350 SDR database would be corrected by replacing light globes, resetting a computer, or resetting a oxygen panel, all of which are standard maintenance tasks.
The reality is the vast majority of SDRs are discovered during routing maintenance and rectified using published procedures. The worldwide SDRs reports is one of the tools the MRB uses to modify the MPD for the type, the OEMs also use them to develop service bulletins.