Demonstrably is a synonym of attestably.
As adverbs the difference between demonstrably and attestably
is that demonstrably is in such a manner as to be capable of being demonstrated, shown or proved while attestably is in an attestable way.
demonstrably
English
Adverb
(
en adverb)
In such a manner as to be capable of being demonstrated, shown or proved.
attestably
English
Synonyms
* demonstrably
* provably