"widely attested" is a correct phrase and can be used in written English.
It is typically used to indicate that something has been observed, experienced, and documented by many people. For example, "The effectiveness of this new treatment is widely attested."
(Who else?) Whereupon, as is more widely attested, he ran his sword through Troy's aged King Priam.
For example, a number of Nostratic words have been found to be more widely attested (especially in Kartvelian and Afro-Asiatic) than was suspected.
Beckett's small but noble role in the French Resistance authenticated the impression of an existentialist saint, as did his widely attested kindness and remarkable (not to say masklike) courtesy as a person.
Although Hieroglyphic Luwian is more widely attested than Cuneiform Luwian, radical revisions in the understanding of many hieroglyphic signs have shown that the two written forms of the language represent two very similar dialects whose precise relationship requires further research.
Traditionally, the term was strongly associated with epic singing in Serbia and Montenegro, but it also was widely attested in the historic regions of Bosnia (now, like Herzegovina, part of Bosnia and Herzegovina), Croatia, Dalmatia, and Herzegovina.
Note that a stationary applied object is widely attested across many languages.
A lack of conceptual clarity — attested by widely-varying definitions — can inhibit understanding of maternal-fetal relationships [ 25- 27].
The need for wider and more systematic dissemination of experimental proteomics data is widely recognised, as argued in [ 27], and attested to by the ongoing work of the Proteome Standards Initiative [ 3].
Common English colloquialisms attest to widely held beliefs about the relationship between height and social status: We "look up" to higher status people, who may be characterized as "elevated," having reached the "height of power," "standing head and shoulders" above their peers, or simply being "giants" among them.
The presence of the Etruscan people in Etruria is attested by their own inscriptions, dated about 700 bce; it is widely believed, however, that the Etruscans were present in Italy before this time and that the prehistoric Iron Age culture called "Villanovan" (9th 8th century bce) is actually an early phase of Etruscan civilization.
He let a widely-attested fact of recent history make the case for him the conversion of the Khazar kingdom to Judaism almost four centuries earlier.
