File dividers - "Mc" but not "Mac" or "O'"?

I’ve wondered this for awhile (and didn’t find anything in ‘search’).

With “A-Z” file or 3-ring binder dividers, why is there a separate divider for names beginning with “Mc”? I once found a set with a separate divider for “Mac” but never one for “O’” (O apostrophe). Most businesses and libraries I have worked for file names begining with “Mc” after “Mb”, not as a different file from the "M"s collectively. So why is “Mc” treated differently from other surname prefixes, say “della” or “du” or “al-” or “von”?

Because Mc is pronounced “Mac”, and also because it’s part of the name, while della, du, al- or von are. Howard McPhillips is called Mr. McPhillips, but Howard von Blaustein is called Mr. Blaustein.

I think the idea is to use “Mc” for both “Mc” and “Mac” so that they don’t get screwed up due to not knowing how the person spells their name. Because there are lots of ways: McUppercase, MacUppercase, Mclowercase, Maclowercase, Mac Separate, Mc Separate…

Personally, I’m a McUppercase.

Cap’n: Are you sure? I’m pretty sure that Gianni del Corso is Mr. del Corso.

British usage traditionally separated “Mac” and “Mc” from the rest of the M’s when filing by name. I’m not really sure why, but they wanted to differentiate betwen “Macon” and “MacInnes.”

The difference is not observed in the U.S., and seems to be fading out in the U.K. as well.

Yep. It’s part of the name. It might be common practice to leave it off for filing purposes, though. It makes sense to do so, in a way. But it IS part of the name, like matt said.