AppV PackageGroup Version in Registry

When we're updating a Package which is linked to a Packagegroup (CleintConnectionGroup, it configured to use the latest version) the Version GUID of the Packagegroup stays the same, but in Registry another 19-digit-Guid is added after the VersionGUID.

for eg.

HKLM:\SOFTWARE\Microsoft\AppV\Client\PackageGroups\<PackageGUID>\Versions\<VersionGUID>\8889517741598403211\REGISTRY\MACHINE 

Does anyone know how this ID is generated? 

I couldn't find any Information about this in ID anywhere