Bill,
Thank-you for researching this. My understanding was that the very earliest vehicles were delivered first to the Long Beach West Coast port, that there was not a simultaneously opened East Coast port in the beginning. From reading only, and could be incorrect.
Could you share your source of information on USA plate stamping and the years during which this was done--are you referencing a Toyota document? Curious to know if this was Toyota's delivery requirement worldwide at each country's port of entry and when this ceased. The few foreign non-Japanese assembly plants seems to explain the variances in those "VIN" plates through the years.
Individual stamping would be awkward when the very first few vehicles early started trickling into each country--some must have come directly from Japan with the information pre-stamped, if not in Japanese, then perhaps in some native language if that was an import requirement.
Interested to learn more from your research.