Word for someone ignorant of, but not expected to be knowledgeable about, something

A discussion arose in our office which brought about remembrance of an old term used by William F. Buckley, Jr. — from his old National Review days — in his "Word of the Day." We can't find the term on the Interwebs, so we come to SE:ELU in hopes of enlightenment.

The definition, as we recall is:

"Being ignorant of something of which you have neither reason nor expectation to have any knowledge."

I'd really like a reference to Buckley's WotD if possible since it will be used frequently in my geek- and academic-heavy office!

I think I may have found the term the OP is searching. It is without doubt a word I have never heard of before. It's worth citing the entire Wikipedia article

Ultracrepidarianism

Ultracrepidarianism is the habit of giving opinions and advice on matters outside of one's knowledge.

The term ultracrepidarian was first publicly recorded in 1819 by the essayist William Hazlitt in an open Letter to William Gifford, the editor of the Quarterly Review: "You have been well called an Ultra-Crepidarian critic." It was used again four years later in 1823, in the satire by Hazlitt's friend Leigh Hunt, Ultra-Crepidarius: a Satire on William Gifford.

The term draws from a famous comment purportedly made by Apelles, a famous Greek artist, to a shoemaker who presumed to criticise his painting. The Latin phrase "Sutor, ne ultra crepidam", as set down by Pliny and later altered by other Latin writers to "Ne ultra crepidam judicaret", can be taken to mean that a shoemaker ought not to judge beyond his own soles. That is to say, critics should only comment on things they know something about. The saying remains popular in several languages, as in the English, "A cobbler should stick to his last", the Spanish, "Zapatero a tus zapatos", the Dutch, "Schoenmaker, blijf bij je leest", and the German, "Schuster, bleib bei deinem/deinen Leisten" (the last two in English, "shoemaker, stick to your last")

I was surprised how few online dictionaries specifically list this one...

unconversant - not conversant, unfamiliar, not well-versed
...from negated...
conversant - familiar by use or study (usually followed by with)

In my experience, when people say they're unconversant with X (or not well-versed in X), there's usually the implication that this lack of knowledge is only to be expected (because X is an obscure fact or field of study, for example).

Perhaps that implication flows naturally from the fact of using a relatively obscure term to describe one's ignorance (i.e. - whilst disclaiming specific knowledge of X, the speaker conveys to his audience that he's not "ignorant" in general).

How about layman?

A person without professional or specialized knowledge in a particular subject: 'the book seems well suited to the interested layman' -- Oxford Dictionaries

I seem to remember Buckley distinguishing between ignorance and nescience. Ignorance was not knowing something you should know. Nescience was not knowing something that there was no reason for you to be expected to know.

I never have been able to validate this distinction when I looked in dictionaries, even old editions. I thought one of my pet peeves had struck again. Where ignorant people pervasively misused 'nescience' to the extent that, instead of steadfastly expecting these people to get it right, the dictionary editors insidiously made the incorrect usage correct, thereby causing a significant spike in the number of "knowledgeable scholars" in the general population.

Wait! What? I'm describing our current education system and society in general.