apt-get upgrade question

[Richard Kimber <rkimber@ntlworld.com>]

In the course of a recent Debian testing apt-get upgrade, without using
the -u option, a number of packages were upgraded. I discovered that one
of these turned out to be kernel-source-2.4.19.  Since I only have one
kernel-source-2.4.19 directory on my machine, I assume that it just
overwrote what was there previously.

My questions are: was this an entirely safe procedure?  And, if the files
have been overwritten, how do I find out which release of 2.4.19 I had
previously?

Thanks,
- Richard.