Pottawattamie High Council minutes mentions Oliver Cowdery's rebaptism.
Pottawattamie High Council minutes, November 5, 1848, LR 1764 21, Church History Library
After some more remarks from different ones of the Brethren, the question was called up and Bro. O. Cowdery was received back again into the church, on his being baptized, by a full vote, and many expressed their gratified feelings on the occasion. About 2 o’clock p.m., he was Baptized by the hand of Bro. Orson Hyde.
This indicates that Cowdery was baptized on November 5, 1848.