Piecemeal code deployment v/s Complete source code

[SVN User <sv...@gmail.com>]

This is not a subversion issue, but I thought I might ask it here as some
people might have been past this situation.
We are using a legacy Financial application, which was developed using
Cobol. Since there was no version control tool in the past, we just
implemented Subversion.
The developers here are used to moving only changes to QA & Production, They
do not move the complete Tagged source code.
I wanted to know if anybody still practices this piecemeal method of code
deployment or is it complete source code moved & compiled at once.

Thanks for any input.