As a journalist you should use proper reference to arrive at an answer you can be confident with. In this particular case I woud consider General Motors to be the best reference for this question as they manufactured these cars and thus were responsible for naming the parts. This is otherwise known as nomenclature.(name of the parts)
The correct name for the COWL TAG or TRIM TAG is actually called a "body number plate." The VIN is just called a Vehicle Identification Number without any other word attached to it. I don't see where it would be inappropriate to use the word "plate" following "VIN" as it is a plate. I also think, in my opinion, that when you are writing for general public consumption it is probably better to use the "street terms" so that the reader understands what exactly you are referring to. If you are writing to a group of engineers I would use only the correct technical terms.
Although in our vernacular we may use other names and terms for parts that are considered acceptable this is commonly known as jargon or lingo. I don't know of another area that has more mis-nomers, jargon, lingo and synonyms than the automotive field. Some of the terms we use daily in this business are actually not even accurate to the role of the part. I think the Alternator is one of the most ridiculous. It is actually an AC Generator but Chrysler in the early 1960s coined this name as a marketing tool to introduce their new more powerful Generator. Somehow the name just stuck and we are still using it today. The ignition coil is another one. It's a step up transformer but Henry Ford's model T had a coil that resembled Tesla's coil and it remains firmly in place.
As a former technical editor for automotive publications and instructor for GM I was downright floored at some of the writings I came across. I used to tell my students that the old axiom still holds true: Paper does not refuse ink. I'm impressed that you are seeking this information and want to get it right. That is a real change in the periodical business. They are usually the worst offenders.
I'm going to look for a copy of this magazine and check it out. Will you be writing there soon?