On the Microsoft Dynamics 365 On-Premises Cumulative Updates webpage, there is a Important note near the top of the page which reads:
Important
• Always apply the most recent update.
• Applying an older 9.1 update on a computer with a later 9.0 version will result in failures due to some assemblies not loading correctly.
• If your 9.0 deployment is 9.0.47.08 or later version, then you must apply the 9.1.20.11 update or later version.
The last point specifically reads "If your 9.0 deployment is 9.0.47.08 or later version, then you must apply the 9.1.20.11 update or later version.". This is ambiguous and could be interpreted in one of two ways:
The second option be can interpreted that way since the Important note could be considered to be in the v9.1 branch section of the page.
If the first option is the correct interpretation then why release v9.0 updates beyond v9.0.47.08? In fact, there are updates on the v9.0 branch running all the way up until November 2023. But, while the January 2024 update has been published on the v9.1 branch, this is missing from the v9.0 branch. Does that suggest support has ended for v9.0, or that the update has been delayed or not necessary?
Either way, the instructions are unclear and are ambiguous, which has caused some concern within our business as to which path to take, especially since our current version is v9.0.48.8. I would be grateful for an official steer on this.
Kind regards
Kaine
What the documentation is trying to explain is when upgrading from CRM 9.0 to CRM 9.1 for an on premises deployment currently on version 9.0.47.08 or later, update 9.1.20.11 should not be skipped.
I.e. when your CRM 9.0 deployment is on Update 0.51 (todays most recent) and you want to upgrade to the most recent CRM 9.1 version you should follow these steps:
Occasionally cumulative updates are not perfectly cumulative...