A validation issue was addressed with improved logic. This issue is fixed in macOS Catalina 10.15, iOS 13.1 and iPadOS 13.1, tvOS 13, watchOS 6, iOS 13. A local app may be able to read a persistent account identifier.
https://support.apple.com/en-us/HT210634
https://support.apple.com/en-us/HT210607
https://support.apple.com/en-us/HT210606