Maybe Baha'u'llah was all-knowing. The following passage seems to indicate that.
“O KING! I was but a man like others, asleep upon My couch, when lo,
the breezes of the All-Glorious were wafted over Me, and taught Me the knowledge of all that hath been. This thing is not from Me, but from One Who is Almighty and All-Knowing. And He bade Me lift up My voice between earth and heaven, and for this there befell Me what hath caused the tears of every man of understanding to flow.”
Proclamation of Bahá’u’lláh, p. 57