I have multiple machines running 11.5.1 (Big Sur) enrolled in the Developer Program, as well as two running 12 under Monterey in the Developer Program. Not one of the machines running 11.5.1 has shown the update to 11.5.2 anywhere in the past 7 or 8 days since 11.5.2 was released. Is it possible that the 11.5.1 (from the developer site) is really a slip-streamed 11.5.2 without the version number. Digging into the system information, my 11.5.1 shows as version 20G80. The 11.5.2 full installer is available on the App Store, but I really don't want the downtime of installing a full version if unnecessary.
