Oliver Cowdery was used to writing the singular him since up to now in the olive tree allegory there had been only one servant that the Lord of the vineyard had been speaking to. From verse 7 through verse 57, there are 19 instances where the text refers to the Lord speaking to this servant, although only one of these instances uses the pronoun him to refer to the servant (in verse 22: “and the Lord of the vineyard saith unto him”).
This copying error involving him and them occurs only once in the olive tree allegory, here in verse 71. For the rest of the olive tree allegory, Oliver Cowdery correctly wrote them in 𝓟 without any initial error, as in the following instance of “saith unto them”:
Of course, the nearby occurrence of his servants in this sentence made it easier to avoid the error.
Summary: Maintain the plural pronoun them in Jacob 5:71 since the context here clearly refers to more than one servant.