The short answer is no, for two reasons:
1. Some items such as moldings, whether steel (including stainless) or aluminum, provided no good way to hide from view any identification stamping, so that makes the "all" part of the question false.
2. While most parts were "identified" in some manner, not all of them were "stamped". Some were cast (cast engine components), some had a tag attached (seats), some were painted, some had stickers.