If truth values are simply the referents of sentences in Frege's semantic scheme, then distinguishing them 'from' senses merely restates the sense/reference distinction rather than establishing truth values as independently ontologically significant.

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Frege(as a major historical figure in philosophy): Gottlob Frege (1848-1925) was a German logician and philosopher who founded modern logic and did groundbreaking work on how language relates to meaning and existence.
Ontologically significant(as describing whether truth values exist as their own category of things): Important or meaningful in terms of what actually exists; something that deserves to be considered as a real, independent thing rather than just a side effect of something else.
Referents(as used in logic and semantics): The actual things or objects that a word or term points to or stands for in the real world.
Semantic scheme(as Frege's framework for understanding meaning): A theory or system that explains how words and sentences get their meaning and what they refer to in the world.

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