I'm looking at the chart in the InstallShield Knowledge Base article Q105413.
It basically shows:
Minor Upgrade:
- change package code
Minor Upgrade with Patch:
- change Package Code
- change Product Version
Major Upgrade:
- change Package Code
- change Product Version
- change Product Code
Upgrade Code is the final column and is never used.
The only real reference I could find for Upgrade Code was in the MSI Help Library.
From what I can make out, the Upgrade Code is VERY poorly named by Microsoft and really should be the "Master Code" (or something).
If you change this, you are dealing with something really completely different that has nothing to do with anything you've worked on before.
Can anyone verify this? Do I understand it correctly?