3) On your final comment sleepy, I was wondering, do you prefer "data are" or "data is"?
I'm slowly getting used to data are, having been committed to "data is", for years. Apparently the Times still uses both. The example you were wondering about seems more natural for me to use the plural because the reference to the "collection of ex-presidents". With data, I guess I've always been used to viewing it as singular.
I have to admit, although it makes my prescriptivist fairy cringe, that my ear prefers "data is". Thing is, you almost never hear "datum", but I suppose that would be "datum is". Sometimes ya just gotta throw up your hands and go with your gut! :0)
Oh, but "collection" is singular, and is the subject, whereas "of ex-presidents" is only the modifier. If you drop the modifier, are you still comfortable? "...the only people that know are the collection we have."
