Ok did some more checking, it looks like VST Inventory is pulling the list from
HKEY_CURRENT_USER\Software\Cakewalk Music Software\SONAR Producer\Cakewalk VST X64
But Sonar Platinum's list appears to be in
HKEY_CURRENT_USER\Software\Cakewalk Music Software\SONAR\Cakewalk VST X64
So it's showing me my X3 plugins, which I haven't started/updated in a while.