(Get-SPFarm).BuildVersion will not tell us if a specific CU has been installed, only those patches which include schema changes for the SharePoint config DB update this information.
To check if your CU has been installed successfully, please go to Manage Patch Status page on SharePoint CA> Upgrade and Migration> Check product and patch installation status:
More information for your reference:
https://blog.stefan-gossner.com/2016/08/23/sharepoint-does-not-have-a-build-version-full-stop/
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