[noun] + (だ)と言えなくもない [na-adj] + (だ)と言えなくもない [i-adj] + と言えなくもない [verb (plain)] + と言えなくもない
と言えなくもない means "you could say that, I suppose": you grant a claim some truth without fully backing it. It follows a plain-form sentence, and a noun or な-adjective can take だ before と or go without it. The form is a double negative: いえない言えない "can't say" plus なくもない "it's not that … not".
The reservation is usually spelled out next, after が or けど.
The pattern belongs to discussion, reviews and essays. In conversation it shows up softened with ね, as a reluctant concession: まあ、ただしい正しいといえなく言えなくもないね.