Do all mirrors in mirrors_full contain all distributions?

[Lloyd Zusman <ljz@asfast.com>]

I'm trying to understand the use of the `mirrors_full' file in the
`netselect-apt' utility, and I realize that there's a gap in my
knowledge.  I couldn't locate the information to fill this gap in any
documentation that I've been able to find, so I'm asking here.

Is each and every site listed in the `packages over HTTP:' lines in
`mirrors_full' guaranteed to contain all distributions (`stable',
`testing', `unstable', etc.), or do certain sites only contain a subset
of these distributions?

If the latter is true, what is the most net-efficient method (i.e.,
requiring the fewest queries over the internet) for determining which
sites in `mirrors_full' contain any given distribution?

Thanks in advance.

-- 
 Lloyd Zusman
 ljz@asfast.com