Brian C. Hales reviews Joseph's sealing to Sylvia Sessions. Concludes they were sealed in late 1842–early 1843 and most likely did not have sexual relations.
Brian C. Hales, "The Joseph Smith-Sylvia Sessions Plural Sealing: Polyandry or Polygyny?" Mormon Historical Studies 9, no. 1 (2008): 41–57
In this article Brian C. Hales gives a detailed examination of the marriages and children of Sylvia Sessions Lyon. Because of certain actions on the part of Windsor Lyon, her husband, Hales feels that Sylvia Sessions should not be included on the list of plural wives of the Prophet Joseph Smith who could have been living in polyandry, that is one wife with more than one husband.