The determination of left & right has been an industry standard for well over three centuries, yes, dating well back to the horse drawn era, & possibly even back to Roman times for all I know.

Calling the 1200 engine an A12 is technically correct, however the designation also includes the later, different A12's, creating confusion, particularly when relating to those parts that were changed between the two designs, like alternator mountings.
Refering to the engine that was used in the Datsun 1200 up to 1973 as a '1200' engine removes all possible confusion & avoids needless explanation later.

Sorry for being a pedant, but it's one of those character traits that you all know & love me for. [Yeah, ... right]