The phrase "otherwise attested" is correct and usable in written English.
You can use it to describe something that has been certified or verified in other ways. For example, "The authenticity of the documents was otherwise attested by a third-party witness."
Though there is less history and more legend, much of the atmosphere of an older age is preserved, with the patriarchs represented as seminomadic, essentially peaceful and pastoral tent dwellers alien residents—among the settled Canaanites and as observing customs otherwise only attested in Mesopotamia.
With this study which can otherwise be attested as having a good study quality, the proof of efficacy for 12.5 and 25 mg diclofenac potassium is yielded for the acute treatment of tension-type episodic headache.
Swimming in deep water off Hawaii inspires in him a terror that passes only after he scampers — "You might think that it would be impossible to scamper in flippers, but I can attest otherwise" — back aboard the catamaran, where he stays.
Divorce statistics and the stories of unhappy marriages seem to attest otherwise for a large group of people.
Fifty-one bishoprics are attested for Egypt in 325; fifteen are only known otherwise as seats of the schismatic Church.
Though the most lyrical passages in Mr. Naipaul's otherwise flatly written letters attest to his nostalgia for home ("I long for the nights that fall blackly, suddenly, without warning," he writes his father. "I long for a violent shower of rain at night"), he remains contemptuous of Trinidad as one of those countries he would later describe as "half-made" societies "doomed to remain half-made".
In historical linguistics, reconstructed (or otherwise unattested) forms are preceded by *, to distinguish them from forms which have been attested in speech or writing.
The players attested to that.
Ms. Parton attested: "He has been!
His circumstances attested to those hopes.
