How Can I Distinguish Between Stake That I Personally Added to a Validator and Stake That I Acquired Through Other Means?

You can’t.  There’s no longer a link between an amount of stake on a validator and a particular account.  If knowing such a thing is important to you, and you participate in activities other than staking which result in you acquiring Liquid Stake Units, you’ll have to reconstruct that information from your transaction history, use separate accounts, or take advantage of a service which does it for you.

Further Reading:

• Start Here! Radix Staking Introduction
• How does staking work on Radix?
• How do XRD emissions work?

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