Interesting that in the North American book it says they the letter 'L' combined with the letter 'U' further along in the string [L-U] is for US & Canadian models.
In reality, the letter 'L' is for 'left drive' while the letter 'U' is for vehicles destined for North America in the same way that 'X' is for Aussie spec models.

Left drive models, all of which carried the 'L' code were sold into many other countries as well, so what the book says is not 'untrue' but not entirely accurate either.

My book says "The unit & car numbers are stamped & registered at the factory.
The engine & car identification numbers are used on legal documents. These numbers are used for factory communications such as Technical Report, Warranty Claims, Service Journal & other information."

The only image that I have that relates to my stepfathers Datsun dealership is on a colour slide [transparency] & it shows a white 1200 coupe [like I drive now] in the showroom.
He was a half owner of D&G motors in Blacktown [Daniels & Grimshaw] & he was the 'D' part.