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AI support's response in these threads has been that the user needs to change the Product Code and the Upgrade code, with the reasoning being that Windows requires this and doesn't allow two products with the same Product Code to be installed. But this isn't a new product, it's merely an update of the same product with minor changes and patches.
We've never had trouble with this until AI, and the more I research, the more I discover that AI's requirement isn't correct. You should never, ever change the product code unless you consider the new version to warrant considering it a different product from the last product code (like Microsoft Word 2003 and 2007), and you shouldn't change the Upgrade Code for minor changes or patches. And I'm certainly not installing a new product, I'm installing an update; the name is exactly the same, and I only changed the build or minor version (3rd and 4th segments) in my tests.
Furthermore, my company has gone from using two different major installer programs for over 10 years to now using Advanced Installer in the past couple of months. With the previous programs, after setting up the installer for each product with a unique Product Code and Upgrade Code, we never once had to touch these GUIDs again. This includes multiple products with many updates across multiple years. With past installer programs, all we do is provide the new files to install, update the version number (which never yields a warning about changing the GUID in these programs), and build, and the installer runs perfectly and overwrites the files regardless of the product and upgrade codes not changing. Running the installer for an older version or newer version, or the same version, never required uninstalling the product for the installation to proceed, either.
Why can't Advanced Installer simply just overwrite the files for a product when we just need to release bug fixes via the installer? Is the intended use of AI purely for initial setup of a product, and not for updating a product with future installer builds? Our current method has us doing full reinstalls of the product for each update for our own reasons. Surely there's a way around this, because it isn't normal or correct to have to change these GUIDs just because the version changed.