A Dozen of

This depends upon the accuracy of the writer. Some writers use "dozen" to mean "roughly a dozen." (In the neighborhood of ten). I suspect that the writee does not actually mean 12. If the writer does not mean 12, and wishes to be accurate, there are better word choices: a group, many, several.
Also, what does the phrase "denied the archive" mean? An archive is a collection.

Not necessarily a Dozen...

Contextually speaking what the writer meant was, "Many of her scholars denied the Archive", you may ask why he used A Dozen of rather than Many of.... that is because, while writing an article which is read by many people, the writer (Journalist) has to provide convincing news, and it should not seem that whatever he is writing, he himself

Thank you for your answer. It helped me a lot.

Doctor DAlso, what does the phrase "denied the archive" mean? An archive is a collection.

I checked the original magazine and found that the word that was used was "denounce."

Then, can an archive can be denounced?

If you can't deny the archive, how can you denounce the archive?

wh

You can denounce an archive as poorly conceived, poorly or inaccurately stocked, etc, or as here, not authentic but fake possessions of Frida Kahlo. The archive is the collection itself of her items found in the trunks in the antique shop.

nice to see you again, and many thanks.

so, am I right in saying that the archive can mean a collection of something which does not have to be in a paper form?

Because my dictionary says that "The archive or archives are a collection of documents and records that contain historical information. You can also use archives to refer to the place where archives are stored."

On re-reading, I've changed my mind grammatically. Here is the relevant passage:

Yet it wasn’t until 2009, when The New York Times announced the forthcoming publication of Finding Frida Kahlo, a book cataloging this eclectic collection, that the art world took notice—and not in a good way. A dozen Kahlo experts signed a letter denouncing the archive.

Oh! this makes perfect sense.

I kind of thought that way, although it was not clear enough.

Thank you for your help.

It means a lot to me.