Somethings being lost in translation here.
Take the Cessna seat belt issue - lets say a 1977 Cessna 172.
The Cessna 172 Service manual states it is Cessna who have established the 10 year life. Not the FAA. Its therefore a TC holders recommendation and as such subject to evaluation for inclusion in LAMP just as your flowchart says.
There are no Airworthiness limitations or Life Limitations for a 1977 Cessna 172 either in the service manual or in the TCDS.
Take another for instance - American Champion 8KCAB Dekathlon.
This does have an Airworthiness Limitation in the Service Manual for the wing strut fittings being lifed at 1000 hours. However, without any FAA mandatedness it really means nothing & could be ignored as a manufacturers recommendation if desired, so the FAA include it in the TCDS to make it mandatory, and thus that one is required to be added to LAMP.
I think you (or your surveyor) are confusing CAA/FAA/EASA mandatedness with a manufacturer just saying mandatory to cover his backside.