Debian Repository Question

[gooldi <damalakim@lavabit.com>]

Hi,

I have a question about the way packages are handled in Debian. I am 
used to CentOS/Fedora Repositories.

My Problem:
*I have a Package Z that has a dependency on a "Package X Version Y1" in 
the Repository.
*Package X Version Y1 is updated to version Y2 in the Repository.
*My dependency is broken.

My questions are:
*Where do the old (Y1) packages land? or are the thrown out of the 
Repository?
*What do the revisions actually mean? (4.0r3) Because there is no way to 
get to the packages of lets say 4.0r2.

Thanks

-Tom