The phrase "are not attested" is correct and usable in written English.
It can be used in contexts where you want to indicate that something has not been documented or verified.
Example: "Many of the claims made in the report are not attested by any credible sources."
Alternatives: "are not documented" or "are not verified".
Many of these Proto-Tai traits are not attested in modern Tai languages.
It is possible that the same observation applies to some of those modern Iranian languages that are not attested in the earlier periods.
A few ideas expressed in this work are not attested in any other known sources.
It has been shown that applicatives are consistently merged above VP in Tsou and that low applicatives are not attested in the language.
But there are problems with this attribution, most notably that the term anathumiaô and its cognates are not attested until Aristotle, and are not the kind of words we find Heraclitus using.
It is a striking observation, however we explain it, that the forms of particular things which coexist in the mind of Origen's God with the genera and species are not attested in any pagan Platonist before Plotinus, his younger contemporary and (as most believe) a fellow-pupil of Ammonius Saccas (cf. Plotinus, Enneads 5.7).
The haoma cult was practiced at Persepolis, but animal sacrifice is not attested.
According to the Oxford English Dictionary, the latter sense is not attested in English until after Knox's death.
(An asterisk before a letter or word indicates that the sound or word is not attested but is a hypothetical, reconstructed form).
But there is little supporting evidence for this claim, and the presence of Dravidian speakers throughout the whole subcontinent at any time in history is not attested.
The Pythagorean doctrine of a cyclic universe may also be derived from India, but the Indian theory of cosmic cycles is not attested in the 6th century bce.
