From my test Mac, it looks like these entries are unique on each users keychain. In cases where the machine might have multiple user keychains (like multiple AD integrated logins), I don't think I'll have access to the SfB keychain entries until a user logs into the machine.
Can I trust the Skype for Business client to handle those old keychain entries properly in the case of uninstall/reinstall during launch? Will it clean up/overwrite what it finds for each user's keychain? Or is it better practice to build and deploy a keychain cleanup script that runs for each user during first login after the uninstall/reinstall has completed?