According to my information, James (Jemmie) McClatchey had three wives: Margaret Glenn, Catharine Davis, and Elizabeth (last name unknown). Margaret appears as a head of household in the 1790 census in Derry Twp., Westmoreland Cty, PA in a household comprising one male under 16, one over 16, and four females (one of which would be Margaret Glen). Her first child begot by Jemmie, another James, was born 22 June, 1794, which is likely the source of the date of marriage that you have. She died Sept. 30 1815 and is buried in the church yard of the Union Presbyterian Church in Cowansville, Armstrong Cty, PA.
A James McClatchey appears on the 1792 Derry Twp. tax roll, but it is not clear whether this is Jemmie or his father. If this was Jemmie, it suggests that he may already have been married and a head of household in 1792. I would be interested in hearing your source for the 1794 date for the marriage if it is not as I have surmised, as I have it listed only as circa 1790.