When I deploy a new version of a software package, I add it to the same gpo, and declare which old packages are replaced by this one, so windows installer knows that it's an update, not an additional package.
How long should the old versions remain in the gpo?
Must it stay until no machine has it installed any more?
When happens if it's removed earlier?
What happens if the msi-files are removed earlier, how long are they needed?