Q1. In order to uniquely identify a MS update for all catalogues, do we rely on BOTH the Guid and Revision?
Q2. If answer to Q1 is positive, then its is true that for a certain KB, the Guid will remains constant over time when Microsoft publishes newer revision (10x, 20x..) available to the public?
It is true for a specific update package that the UpdateID (which is a GUID) is static. This statement is not true for a given KB article, because a single KB article may (in fact almost always does) have multiple update packages, depending on which platforms or applications are affected by the update.
Q3. With the same chain of thought, for a Microsoft box that has a Guid with revision 202 installed, and for the same Guid that has 203 becomes available, would windows update able to install revision 203?
The WUA will install the newest revision that is approved. A revision does NOT cause an update to be RE-installed. A revision is merely a change to the metadata or detection logic in an update package. A revision does NOT include a change to the installer file. Ergo, if an update is already installed, regardless of which revision, the fact that a new revision is available is irrelevant -- the *update* has already been installed.
A change in the installer file for an update requires a new update package with a new UpdateID.
Thank you for the confirmation.