How exactly does `make menuconfig' work?

Hi all,

If it's a festive time of year in your part of the world, then I hope
you're enjoying it.

In a freshly unpacked kernel source, if I run:

  $ make allnoconfig

... it generates a minimal config with all options set to `no' which I can
then peruse with `make menuconfig', switching things `on' rather than
`off'.

This sounds fine, but...

... when I did this, there was simply no vesafb graphics option, which
I need.  In fact, the only way I can gain access to this option is to
base my new config on my existing one in /boot (which already includes
it) by expliciting loading it as an `alternative'.

Why is this?

I had been lead to believe that running:

  $ make menuconfig

... in a freshly unpacked kernel source automatically bases the new
config on your existing config.  I thought this was the case until I
came to the missing vesafb option.  I then tried running `make
mrpoper' and copying my config from /boot to the unpacked source
directory (as was suggested in another document) before running `make
menuconfig' again but still no vesafb option!

In short, I'm a little confused.

1) Why doesn't `make allnoconfig' include the veasfb graphics option?
2) Does a clean `make menuconfig' consult /boot/config-x.x.x or not?

I'd be extrememly grateful if someone could provide me with a clear
overview of the `make *config' process.

sdt