Compound last names and the "usually referred to" clause

[dschafer]

From the ACF Rules (emphasis mine):

4.1 Compound last names must be given in their entirety, and a partial last name will not be prompted. E.g., " García Márquez" and "van Buren" are the required parts of the answer for Gabriel García Márquez and Martin van Buren, and answers such as "Marquez" or "Buren" are outright incorrect. It is acceptable to give a partial last name for people with formally compound last names when those people are usually referred to by a part of their name—e.g., "Pablo Picasso" is acceptable for "Pablo Ruiz y Picasso."

How "usually referred to" does a last name have to be before it is acceptable? I bring this up based on the BBC - Homepage today, which includes the following:

A Spanish judge has launched an enquiry into the disappearance of thousands of people in the 1930s and 40s. Mass graves may be dug up, including one thought to contain the poet, Lorca. Find out about this controversial look into the Franco era.

* Franco probe launched
* Lorca's grave to be opened
* About Picasso's 'Guernica'

I've always included Lorca on my personal list of people that I need to give both names for to be safe (and he was specifically referenced as such in the thread discussing the New ACF Rules when this was brought up). If the BBC (and Britannica) refer to him as Lorca, though, should that not be acceptable?

More generally, what is the deciding factor in deciding if a given person is "usually referred to by a part of their name"?

[AlphaQuizBowler]

Similarly, I've seen a book that on the side just said Marquez.

[theMoMA]

Lorca should be acceptable for all Garcia Lorca answers. That's how he's commonly known in Spain and often referred to in scholarship.

[Stained Diviner]

I disagree with the ACF Rule, and it is directly contradicted in instructions to moderators in packets that I write and/or edit.

I think that Buren for Van Buren is a borderline case, since answering Buren shows more ignorance than the other examples, but I firmly believe that Picasso is acceptable, Marquez is promptable, and Lorca is at least promptable.

[Captain Sinico]

Yeah, I don't know. I'd say a credibly authoritative reference source (like Britannica) would seem to supply sufficient evidence for me.

MaS